Need Parsing Text Help

[DMG2000]

Hi:
I am new to perl and cgi, atho am experienced with vb and asp, so bear with me:

I need to take a text file generated from a db of users@domains and I need to accomplish two things:
1>
Seperate the users@domains so that output is like
domain1:user1,user2,user3
domain2:user1,user2,user3
and 2>
Seperately parse the text file into line number variables for each address and group by 5 lines like
@group1
var1 = user1
var2 = user2
var3 = user3
var4 = user4
var5 = var5
@group2
var6 = user6
var7 = user7
so forth indefine till eof

Is there any one who can help me with this please? I have a feeling its something super simple. Thanks!

Shawn (DMG2000)
compute_x@yahoo.com