W510 W7x64 4G: VM best for Win XP? Any XP Compat mode tweaks

[crashnburn]

W510 W7x64 4G: VM best for Win XP? Any XP Compat mode tweaks
W510 Win7x64 4G RAM: Which VM best for Win XP Pro 32 bit?

So we want to run XP on this machine to run some software that doesnt run on Win7 and maybe 64 bit OS.

We used the XP Compatibility Mode but its still not working properly? Maybe it wasn't installed properly so will look into it again.

CLIENT-APP SPECIFIC QUESTIONS:
- Would there be an issue if this Business App was to be able to get on the Office LAN and access the Server (Client-Server App that can also work independently as client only copy of the DB as well.)
- What are Doman\User issues that come / could come up for a Virtual Machine run XP / Compatibility Mode run XP App? Does it have to be provided with appropriate user privileges & authentication etc / username / password etc.

I am wondering which VM to go for if Compatibility mode has limitations that cant be overcome: Virtual PC, VMWare or Sun Virtual Box?

VM SPECIFIC QUESTIONS:
If we went for a full blown VM on it, what would be most:
- CPU / RAM Efficient
- Easiest to get up and running?
- Easiest to use for a layman... (To be used by my Dad for 1-2 of the old business specific apps)