Why can't I access my company's VPN?

You have already tried what I would have tried to start with -- double-checking your VPN client configuration, and verifying that another system with the same configuration and software can successfully access your company VPN. That would seem to narrow the problem down to the actual VPN client software installation on your new laptop. Perhaps something in that client's installation or registry entries got corrupted during your last connection -- for example, by a partial/failed update sent from your VPN gateway to your VPN client.

I would try completely removing the VPN client from your new laptop, rebooting after removal. I'd make sure the Extranet Access Client program folder and registry entries no longer existed after reboot, deleting the empty folder if needed. (If you manually delete anything from your Windows registry, make sure you back up your registry first.) Once you are certain that you have a clean slate, re-install the VPN client and settings supplied by your VPN administrator.

With any luck, that will fix your problem. If you are still unsuccessful, another approach you might try is using the Windows XP restore feature to "roll back" your PC's configuration to a date just prior to the failed VPN session. Caution: You will lose all system updates that have occurred since that restore point, which I am guessing may be quite some time ago by now. Restore is best done immediately after corruption occurs because it can be disruptive if used at a much later date. Use it only if you're really stuck and willing/able to reinstall programs and devices added after the restore date. Search WinXP's "help" for system restore instructions.