Outward VPN from behind SBS2003/ISA2004

I have rejigged my office, and taken out the old XP machine which was connected direct to the router and therefore not part of my domain which I used for VPN connections to my customers.  My intention was to use my laptop (part of my domain) for everything.  I changed the IP address of my network so that it was totally different to thoseof my customers, but when I try to VPN to my customers servers is does not connect.  I have looked in live logging on ISA and there does not appear to be anything showing up there.  I have searched the web including isainsbs and isaserver.org, but I don;t see anything there which I can say answers my problem.  Anyone actually doing this who can give me guidance or point me to an article?  BTW I am using Vista on the laptop, but an XP machine has the same problem.  I am usinf PPTP as the VPN protocol, and all customers have previously been VPN'd into.  Hope you can help.

I found that the Firewall Client was interfering with my VPN connections. Once I disabled the client my connections went through without any problems.