Basically you want an editing suite that supports multiple video tracks. Combine this with some rotoscoping software and you are just about there.
You could do worse than Ulead MediaStudio 7 (complete with Video Paint for the rotoscoping part). Why not try out the 30 day trial from http://www.ulead.com/msp/runme.htm and see if its good for you.
The Adobe Premiere fans on this forum will be able to tell you where to get a trial of that particvular software. Also Abode Premiere Elements is good, and it does the Mattes and Keying required, I don't think it will support the rotoscoping.
PS Don't actually buy MediaStudio as I understand v8 is on the way and the overhaul is (alegedly) quite spectacular)
COMPAQ something or other with 500Gb Boot Disk, 1Tb external Firewire Disk, 4Gb Memory and a super duper sound card, 19" TFT Monitor etc etc etc
Sony TRV33e : Sony TRV310e : Canon XM2
Sony Vegas Studio editions to v11
Remember, there is always more to learn than there is to teach.