Not with what you have in the way of equipment. Your Windoze XP Pro can easily act as an IPSec client, but there's no place to terminate the VPN tunnel. You would need to replace your Netgear WGR614v1 router, with another router capeable of terminating a VPN. You already have a wireless access point so there's no need to replace the DI-624. Possible replacements are: Linksys BEFVP41 DLink DI-804HV, DFL-80, DFL-300 There are others.
In my never humble opinion, this is the right way to play wireless, but there seems to be very little interest in using VPN's in this way from the various manufactories of cheap boxes. Colubris, Sonicwall, and some others, have been pushing VPN over wireless for quite a while, but not Netgear, Linksys, or DLink. Note that a VPN tunnel will exact a rather large 50% preformance hit while WEP/WPA typical eat only 15-20%, which may explain their disinterest.
Also, there's no reason to disable the wireless part of the WGR614v1 just to use the DI-624 as an access point. Turn it back on. Set the SSID to be the same as the DI-614, but use a different non-overlapping channel (1, 6, or 11). Also, turn ON the DHCP server. In the DI-624, turn OFF the DHCP server.