a simple LDE (length-disassembler engine) isn't hard to write, take a few days to digest the intel instruction encoding, and then just follow the chart. everything is pretty straight forward.

you'll be needing 2 tables, 256 byte each, one for normal instructions, and one for 'extended' (0x0f) ones. In those tables, store flags for relevent information, such as the instruction takes its param from modrm bytes, or it's naturally a 1-byte opcode, or maybe it accepts imm32 (such as B8 'mov', etc...)

when you load the opcode, simply match that value with the table, and from there, follow the encoding rules to determine the length. some stuff *may* be somewhat tricky though.

my suggestion would be to read up on:

http://www.pdos.lcs.mit.edu/6.828/2004/readings/i386/s17_02.htm

it's a lot simplier IMO than the intel books, cleaner, and as for table, look for Sang Cho's disassembly/assembly table, avaliable on google.

if you're completely not familiar with the instruction encoding, i suggest you read The Svin's opcode tutorials, avaliable at win32asm boards (boards.win32asmcommunity.com)

hope it helps

-drocon