Everytime I log-on I avast detecects this virus:Win32:Dialer-520
Im using:
Windows 98 SE
Avast!4.7 Home Edition
BitDefender 8 Free Edition
Ad-Aware 6 SE
Spybot: S & D
A-Squared anti Malware
Zone Alarm Firewall(expired today)
When I start the computer I get this error:
SHLDDRV.VXD is missing
When I start Avast! I get this error:

This is the error message I get after the memory check finishes.

This is the error message I get after the first one.
And when I scan with BitDefender 8 Free Edition i finds winnyjy32.dll but doesn't remove or quarantine it.
Please help.