Ok, the prob was the office router was set to 192.168.0.1 and so was my home router.
I logged into my home router and changed it to 192.168.1.1 and then everything worked.
So for anyone coming across this thread here is what I did
Set up VPN on windows 7 machine at office, set router to forward ports for pptp and smb
Also, set router to 192.168.0.1
On home router set to 192.168.1.1
On ipad connect to VPN then use file browser to access remote machines by simply using IP address such as 192.168.0.XX
Now I can access files at office from iPad, etc