Windows XP or 7, 32-biy or 64-bit?

Hello Experts,

I currently need to get a new PC for myself and I have a dilemma.  I’m a programmer in VB 6.0, Classic ASP and Access 2003-07 with VBA/VBS , for which I’m currently using:

-      Windows XP Pro
-      VB 6.0
-      InterDev 6.0
-      QuickBooks 2011 Pro & Payroll
-      Office 2007  Enterprise

I’m aware that this technology is a bit outdated, and know if I try really hard I can find a XP-Compatible, but know as time goes on, it’ll be harder and harder, so I’m trying upgrade some how.

I’ve tried a basic version of Win 7 and it would not install VB & InterDev 6.0 at all, however QB 2011 installs but it takes approx 30min to load vs 5min on XP.

Additionally, I know that Win 7 Pro/Ultimate/Enterprise has XP mode, which claims to accept XP software – will VB6, InterDev6 and Classic ASP run in XP mode?  Will QB load faster? In my case, which would be better: Pro/Ultimate/Enterprise?

Alternately, I have lots of experience in VB6 and Classic ASP, and I’m wondering how difficult will it be to pickup .NET (self-learn, multi-week/month/year course)?  Finally, will my applications work/run/open under Windows 7 32- or 64-bit and open with the latest V. Studio version _____?

Thank you.