Partition size for parallels with XP AND Vista

[bunsco]

Hi all,

just got me a new imac 3.06 (2008) with 500GB HD with parallels and XP.

I dont know what size I should make the parallels partition with 2 windows OS's.

I chiefly want to test and perhaps author websites in widows, with maybe a program or 2 installed - like VisualStudio 2008.

Anyone in this position - anyone suggest a good flexible solution?

thanks for any help.