This really depends on the type of VPN you're trying to connect to. I have had great success with Aventail's SonicWall SSL client (provided by Aventail) and others have reported success with CheckPoint's client in Windows 7.
Check with the VPN manufacturer and see if they offer a client of their own. Many firewalls/VPN's will have proprietary clients that can be configured with a "catch-all" client, but there's usually a manufacturer provided one. Most companies have been quick to update their software for Windows 7, as well.
64-bit ready clients might be a little slower, but again - most are coming around.