Apple has not mentioned whether or not the iPad will support VPN connections. iPhones already have VPN support. Since the iPad will run iPhone OS 3.2, it's likely that VPN support will be included.
The iPhone and iPod touch support the L2TP, PPTP, and Cisco IPSec VPN protocols. iPhone and iPod touch devices running iPhone OS 3.0 or later can use VPN Proxy configurations and VPN On Demand.