system’s unpredictable behaviour

i am maintaining a p4 . 845 glly motherboard and 1.7 ghz processor(intel). modem installed is lucent 56k.i am using win xp as well as win 98. win 98 is absolutely fine where as on boot in xp if i straight go to connect to internet, the system would hang for about 2 minutes . after 2 minutes it is again working normal. if i don’t connect to internet on boot for about 2 minutes or so all the system would work properly including the net connections