Crash while surfing

Anytime I’m connected to the internet my pc crashes after some minutes.I thought it was a problem due to Netscape 4.78,but also with Opera the situation isn’t better.Norton Crash Guard tells me the problem is in Olechannelwnd and sometimes in rnapp.My os is w98 se,processor Amd k6-350,chipset Via Apollo mvp5.I would appreciate any suggestion.Thanks.