Sorted! Yeah your'e right about the multipart roms, each one I tried had two files, I thought they was different types of roms. Anyway, I grabbed that TOSEC collection you mentioned. Every rom I've tried (CRT) now works! Cheers for your help m8 :)
Little tip: There's no need to unzip each rom before you import it. Goto Tools/Manage Emulators/Winvice/Edit then tick the 'Extract rom archives before running' box.
Thanks again :)