Need help with regular expression syntax..

[CapitalWebHost]

I need to parse the following:

aaa_bbb_d_yyyy_mm.ext

aaa = ITM, CPF, FAC, GEN
bbb = almost anything (even more then 3 chars)
d = M,Q,Y,R
yyyy = year
mm = month

I'm terrible at figuring out regexp so I turn to the kind folk of SP to help me.

[CapitalWebHost]

What, no one here knows RegExp?