I cant install VB. net in my laptop. HELP.?

My laptop is acer. with vista os.During my thesis i was able to install VB. net 2008 easily and it works well. after my thesis I decided to uninstall vb.net and reformat my laptop. I switch to windows xp because they say that vista occupies a lot in memory. everything goes well, until such time that I need to install vb 2008 again. The problem is. in the middle of installation it just stop. It has failure message that says.. "Cannot install . NET framework 3.0". At first I thought that it was just in os. so I reformat it again in the 2nd time. Still xp but different version. I mean the first one is "The black edition." and this time with windows xp professional. but the same thing happen. :( I also did ask a help from some of my friends and they told me that it works with them. using the same os that I use. please help. I really need to install vb.net. :(