Now is this what you should call a true friend? I don't tend to think so.
First, the basics. Better scan your hard drive for viruses with AVG Free or some other Anti-virus software and scan for spyware with AdAware 2007. Both can be downloaded for free at
Free Software Downloads and Software Reviews - Download.com
After that, open your Control Panel in the start menu, open Network Connections. Right click your Local Area Connection and all other connections that might be listed and choose to repair them. Then restart your comptuer.
If none of those work, you could try System Restore (start > Programs > Accessories > System Tools) which can undo some other network settings he may have screwed up.
And lastly, upload the HiJackThis file that is in my signature if none of this works.