MSN do throttle download and upload speeds using their MSN service because there are thousands of people online at anyone time all using MSN.

I agree AIM is 100% better for file tranfer, but if you have to use MSN, download Trillian (Google it, it's free) I use it all the time and MSN file transfers seem to be alot faster, plus you can connect to your MSN,AIM,ICQ, IRC and Yahoo accounts and all at the same time so you dont have to have loads of windows open all the time.