You need to separate your "nat 0" and your "crypto" access-list. You have them both set to ACL 101, which tells the PIX that any traffic from 192.168.168.0, going to your PPTP clients (10.0.0.0), should be encrypted and sent to 188.8.131.52, which is why your PPTP users aren't getting any response.
Do the following:
access-list 102 permit ip 192.168.168.0 255.255.255.0 192.168.169.0 255.255.255.0
crypto map tosonicwall 20 match address 102
Leave the 101 access-list as is, and leave the "nat 0" command as is. This will tell your PIX to only encrypt the traffic that it's supposed to, but to not NAT both the IPSec and the PPTP traffic.
Table of ContentsIntroductionVersion HistoryPossible Future
UpdatesDocuments PurposeNAT Operation in ASA 8.3+ SectionsRule Types
Network Object NATTwice NAT / Manual NATRule Types used per SectionNAT
Types used with Twice NAT / Manual NAT and Network Obje...
Table of Contents Introduction:This document describes details on how
NAT-T works. Background: ESP encrypts all critical information,
encapsulating the entire inner TCP/UDP datagram within an ESP header.
ESP is an IP protocol in the same sense that TCP an...