did you check this document:
http://www.cisco.com/warp/public/110/pix_pptp.html
take a look at the example. That should work for 7.0 as well
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Commands to Add to All Versions
In this configuration example, the PPTP server is 209.165.201.5 (static to 10.48.66.106 inside), and the PPTP client is at 209.165.201.25.
access-list acl-out permit gre host 209.165.201.25 host 209.165.201.5
access-list acl-out permit tcp host 209.165.201.25 host 209.165.201.5 eq 1723
static (inside,outside) 209.165.201.5 10.48.66.106 netmask 255.255.255.255 0 0
access-group acl-out in interface outside
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