Do you mean something like this page or this one?
It converts the WEP Hex Key to a WEP Ascii key.
Otherwise you could do it manually according to the table below:
Your example Hex:3666386162 = 36 66 38 61 62 translates to Ascii:6f8ab.
A 41 B 42 C 43 D 44 E 45 F 46 G 47 H 48 I 49 J 4A K 4B L 4C M 4D N 4E O 4F P 5O Q 51 R 52 S 53 T 54 U 55 V 56 W 57 X 58 Y 59 Z 60 a 61 b 62 c 63 d 64 e 65 f 66 g 67 h 68 i 69 j 6A k 6B l 6C m 6D n 6E o 6F p 70 q 71 r 72 s 73 t 74 u 75 v 76 w 77 x 78 y 79 z 7A 0 30 1 31 2 32 3 33 4 34 5 35 6 36 7 37 8 38 9 39 Edit:
However, passphrases to HEX WEP keys are a one way encryption.
You can't get a passphrase from a HEX key.
(basically the 64-bit generator uses XOR's and PRNG to generate 4 keys. 104 bit uses MD5.)
Here is some more information about the key generation.
You can also read about how the HEX keys are generated from page 18 forward in this document.
Because there is no way back to the passphrase from a HEX key, there are 2 things you can do:
Change the keys in your router (assuming you have control over it).
BTW If you have control over the router and it supports WPA or WPA2 it is advised to go with that.Use the HEX key in your connection dialog. Often you can just enter the HEX key.
Sometimes (Apple?) you need to put a$before it.