Interesting and specific problem found. Looks like VIA Ethernet driver have some compotability issues with SP3 and Symantec security products. After installing WinXP SP3 update VPN connection stops working on authorisation phase with SEP installed. Turining off SEP protection doesnt help - only uninstalling.
As it appers Proactive threat protection installes its own network drivers that incompotable with VIA native drivers and so local network pings but traffic fails.
I tryed diffrent ways to bypass this bug but the only way I found is during SEP installation choose not to install Proactive threat protection components. Sure it make protection less effective , but its the only way to make VPN connection funtional.