Configuration for XP and PD6

Hi,
I currently install XP and PD6 on my MBP 13.3 4GB RAM
What make me annoyed is when I run XP, I can't open my another program or the beach ball will come out and make my work even slower.

Does anyone can help me how to configure the right setting or what should I do about this? (besides upgrade my RAM to 8GB )

or should I install W7?

Other question, does PD Upgrading to W7 can work on PD6 to upgrade my XP to 7?
Thanks for anyone who can help.