browser hangs in downloads

hi folks,

have xp/sp3 with 768Ram & 400meghz...have turned off windows firewall and do
not have antivirus at the moment (trying to rule them out)...

both IE8 (set to all default values) and Firefox will hang during any
significant download. Streaming video in example always hangs....but so will
just some web pages that are particularly busy.....browses fine for most
other sites for awhile but will also sometimes just hang.

when can't reach a site - xp will pop up offer network diagnostic feature -
- and that will clear up the problem (though a download has to restart from
beginning and still will never complete...

I ruled out IE8 by trying Firefox....and I don't really think it is a
virus........have looked at the logs offered during the Network Diagnostics
and I see a line about semaphore timeout...

anyone knowing about this? would really appreciate some help on this....