Info gathered from: http://sysopt.earthweb.com/articles/win2kpass/index.html 
Credit goes to Scott Crawford (I have no e-mail address for this person, he is who was listed in the article)

NT passwords can contain special Alt-Characters. These are created by holding down the Alt key
and typing a number on the numerical keypad. The advantage of this is that it adds a great
number of combinations to the range of passwords.L0pht crack has been used with great success in
cracking NT passwords. However passwords which have Alt-characters that do not correspond to
regular keys, are uncrackable by L0pht, even when knowing which Alt-Characters have been used. The
files are best viewed in the Lucida Console font.

Alt - 0 = NUL
Alt - 1 = ☺
Alt - 2 = ☻
Alt - 3 = ♥
Alt - 4 = ♦
Alt - 5 = ♣
Alt - 6 = ♠
Alt - 7 =
Alt - 8 = ◘
Alt - 9 = ○
Alt - 10 = ◙
Alt - 11 = ♂
Alt - 12 = ♀
Alt - 13 = ♪
Alt - 14 = ♫
Alt - 15 = ☼
Alt - 16 = ►
Alt - 17 = ◄
Alt - 18 = ↕
Alt - 19 = ‼
Alt - 20 =
Alt - 21 =
Alt - 22 = ▬
Alt - 23 = ↨
Alt - 24 = ↑
Alt - 25 = ↓
Alt - 26 = →
Alt - 27 = ←
Alt - 28 = ∟
Alt - 29 = ↔
Alt - 30 = ▲
Alt - 31 = ▼
Alt - 32 = SPACE
Alt - 33 = !
Alt - 34 = "
Alt - 35 = #
Alt - 36 = $
Alt - 37 = %
Alt - 38 = &
Alt - 39 = '
Alt - 40 = (
Alt - 41 = )
Alt - 42 = *
Alt - 43 = +
Alt - 44 = ,
Alt - 45 = -
Alt - 46 = .
Alt - 47 = /
Alt - 48 = 0
Alt - 49 = 1
Alt - 50 = 2
Alt - 51 = 3
Alt - 52 = 4
Alt - 53 = 5
Alt - 54 = 6
Alt - 55 = 7
Alt - 56 = 8
Alt - 57 = 9
Alt - 58 = :
Alt - 59 = ;
Alt - 60 = <
Alt - 61 = =
Alt - 62 = >
Alt - 63 = ?
Alt - 64 = @
Alt - 65 = A
Alt - 66 = B
Alt - 67 = C
Alt - 68 = D
Alt - 69 = E
Alt - 70 = F
Alt - 71 = G
Alt - 72 = H
Alt - 73 = I
Alt - 74 = J
Alt - 75 = K
Alt - 76 = L
Alt - 77 = M
Alt - 78 = N
Alt - 79 = O
Alt - 80 = P
Alt - 81 = Q
Alt - 82 = R
Alt - 83 = S
Alt - 84 = T
Alt - 85 = U
Alt - 86 = V
Alt - 87 = W
Alt - 88 = X
Alt - 89 = Y
Alt - 90 = Z
Alt - 91 = [
Alt - 92 = \
Alt - 93 = ]
Alt - 94 = ^
Alt - 95 = _
Alt - 96 = `
Alt - 97 = a
Alt - 98 = b
Alt - 99 = c
Alt - 100 = d
Alt - 101 = e
Alt - 102 = f
Alt - 103 = g
Alt - 104 = h
Alt - 105 = i
Alt - 106 = j
Alt - 107 = k
Alt - 108 = l
Alt - 109 = m
Alt - 110 = n
Alt - 111 = o
Alt - 112 = p
Alt - 113 = q
Alt - 114 = r
Alt - 115 = s
Alt - 116 = t
Alt - 117 = u
Alt - 118 = v
Alt - 119 = w
Alt - 120 = x
Alt - 121 = y
Alt - 122 = z
Alt - 123 = {
Alt - 124 = |
Alt - 125 = }
Alt - 126 = ~
Alt - 127 = ⌂
Alt - 128 =
Alt - 129 =
Alt - 130 =
Alt - 131 =
Alt - 132 =
Alt - 133 =
Alt - 134 =
Alt - 135 =
Alt - 136 =
Alt - 137 =
Alt - 138 =
Alt - 139 =
Alt - 140 =
Alt - 141 =
Alt - 142 =
Alt - 143 =
Alt - 144 =
Alt - 145 =
Alt - 146 =
Alt - 147 =
Alt - 148 =
Alt - 149 =
Alt - 150 =
Alt - 151 =
Alt - 152 =
Alt - 153 =
Alt - 154 =
Alt - 155 =
Alt - 156 =
Alt - 157 =
Alt - 158 = ₧
Alt - 159 =
Alt - 160 =
Alt - 161 =
Alt - 162 =
Alt - 163 =
Alt - 164 =
Alt - 165 =
Alt - 166 =
Alt - 167 =
Alt - 168 =
Alt - 169 = ⌐
Alt - 170 =
Alt - 171 =
Alt - 172 =
Alt - 173 =
Alt - 174 =
Alt - 175 =
Alt - 176 = ░
Alt - 177 = ▒
Alt - 178 = ▓
Alt - 179 = │
Alt - 180 = ┤
Alt - 181 = ╡
Alt - 182 = ╢
Alt - 183 = ╖
Alt - 184 = ╕
Alt - 185 = ╣
Alt - 186 = ║
Alt - 187 = ╗
Alt - 188 = ╝
Alt - 189 = ╜
Alt - 190 = ╛
Alt - 191 = ┐
Alt - 192 = └
Alt - 193 = ┴
Alt - 194 = ┬
Alt - 195 = ├
Alt - 196 = ─
Alt - 197 = ┼
Alt - 198 = ╞
Alt - 199 = ╟
Alt - 200 = ╚
Alt - 201 = ╔
Alt - 202 = ╩
Alt - 203 = ╦
Alt - 204 = ╠
Alt - 205 = ═
Alt - 206 = ╬
Alt - 207 = ╧
Alt - 208 = ╨
Alt - 209 = ╤
Alt - 210 = ╥
Alt - 211 = ╙
Alt - 212 = ╘
Alt - 213 = ╒
Alt - 214 = ╓
Alt - 215 = ╫
Alt - 216 = ╪
Alt - 217 = ┘
Alt - 218 = ┌
Alt - 219 = █
Alt - 220 = ▄
Alt - 221 = ▌
Alt - 222 = ▐
Alt - 223 = ▀
Alt - 224 = α
Alt - 225 =
Alt - 226 = Γ
Alt - 227 = π
Alt - 228 = Σ
Alt - 229 = σ
Alt - 230 =
Alt - 231 = τ
Alt - 232 = Φ
Alt - 233 = Θ
Alt - 234 = Ω
Alt - 235 = δ
Alt - 236 = ∞
Alt - 237 = φ
Alt - 238 = ε
Alt - 239 = ∩
Alt - 240 = ≡
Alt - 241 =
Alt - 242 = ≥
Alt - 243 = ≤
Alt - 244 = ⌠
Alt - 245 = ⌡
Alt - 246 =
Alt - 247 = ≈
Alt - 248 =
Alt - 249 = ∙
Alt - 250 =
Alt - 251 = √
Alt - 252 = ⁿ
Alt - 253 =
Alt - 254 = ■
Alt - 255 = BLANK
Alt - 0127 = 
Alt - 0128 =
Alt - 0129 =
Alt - 0130 =
Alt - 0131 =
Alt - 0132 =
Alt - 0133 =
Alt - 0134 =
Alt - 0135 =
Alt - 0136 =
Alt - 0137 =
Alt - 0138 =
Alt - 0139 =
Alt - 0140 =
Alt - 0141 =
Alt - 0142 =
Alt - 0143 =
Alt - 0144 =
Alt - 0145 =
Alt - 0146 =
Alt - 0147 =
Alt - 0148 =
Alt - 0149 =
Alt - 0150 =
Alt - 0151 =
Alt - 0152 =
Alt - 0153 =
Alt - 0154 =
Alt - 0155 =
Alt - 0156 =
Alt - 0157 =
Alt - 0158 =
Alt - 0159 =
Alt - 0160 = BLANK
Alt - 0161 =
Alt - 0162 =
Alt - 0163 =
Alt - 0164 =
Alt - 0165 =
Alt - 0166 =
Alt - 0167 =
Alt - 0168 =
Alt - 0169 =
Alt - 0170 =
Alt - 0171 =
Alt - 0172 =
Alt - 0173 =
Alt - 0174 =
Alt - 0175 =
Alt - 0176 =
Alt - 0177 =
Alt - 0178 =
Alt - 0179 =
Alt - 0180 =
Alt - 0181 =
Alt - 0182 =
Alt - 0183 =
Alt - 0184 =
Alt - 0185 =
Alt - 0186 =
Alt - 0187 =
Alt - 0188 =
Alt - 0189 =
Alt - 0190 =
Alt - 0191 =
Alt - 0192 =
Alt - 0193 =
Alt - 0194 =
Alt - 0195 =
Alt - 0196 =
Alt - 0197 =
Alt - 0198 =
Alt - 0199 =
Alt - 0200 =
Alt - 0201 =
Alt - 0202 =
Alt - 0203 =
Alt - 0204 =
Alt - 0205 =
Alt - 0206 =
Alt - 0207 =
Alt - 0208 =
Alt - 0209 =
Alt - 0210 =
Alt - 0211 =
Alt - 0212 =
Alt - 0213 =
Alt - 0214 =
Alt - 0215 =
Alt - 0216 =
Alt - 0217 =
Alt - 0218 =
Alt - 0219 =
Alt - 0220 =
Alt - 0221 =
Alt - 0222 =
Alt - 0223 =
Alt - 0224 =
Alt - 0225 =
Alt - 0226 =
Alt - 0227 =
Alt - 0228 =
Alt - 0229 =
Alt - 0230 =
Alt - 0231 =
Alt - 0232 =
Alt - 0233 =
Alt - 0234 =
Alt - 0235 =
Alt - 0236 =
Alt - 0237 =
Alt - 0238 =
Alt - 0239 =
Alt - 0240 =
Alt - 0241 =
Alt - 0242 =
Alt - 0243 =
Alt - 0244 =
Alt - 0245 =
Alt - 0246 =
Alt - 0247 =
Alt - 0248 =
Alt - 0249 =
Alt - 0250 =
Alt - 0251 =
Alt - 0252 =
Alt - 0253 =
Alt - 0254 =
Alt - 0255 =

Here are the Characters that were not cracked:

Table of Uncrackable Alt-Characters