I wouldn't say your in over your head. SME 5.5 should handle this fine. Although if you want always on connections, I would probably look at IPSEC instead of PPTP. I've never setup permanent connections, but alot of folks who do prefer IPSEC for this. As for PPTP, do this:
Go into your server-manager and enable the amount of PPTP connections you want. Hopefully you left space at the end of your dhcp scope for this (I never go above .240) since I've heard e-smith uses the unused ones for dhcp, but I never had a problem here either.
Next, make sure your Win2k boxes have SP2 as a minimum and you are set. Create the pptp connection in Network and Dial-up Connections, enter your ip address, username and password and see if you connect. That's all!
As for your access database, you could always look to port it to mySQL, which is already on your e-smith.