I have a few clients on my network that can connect to my work VPN (Windows PPTP) when they are not on my home network.

On my home network (Cable Modem with Time Capsule providing Wifi), it fails very early -- looks like it can't even establish a connection. Logs just say that it failed -- even verbose logs don't have much:

I redacted the host and IP from this log, but I can ping it.

Wed Feb  2 14:32:41 2011 : PPTP connecting to server 'XXX.XXX.com' (XXX.XX.XX.XX)...
Wed Feb  2 14:32:41 2011 : PPTP connection established.
Wed Feb  2 14:32:41 2011 : using link 0
Wed Feb  2 14:32:41 2011 : Using interface ppp0
Wed Feb  2 14:32:41 2011 : Connect: ppp0 <--> socket[34:17]
Wed Feb  2 14:32:41 2011 : sent [LCP ConfReq id=0x1 <asyncmap 0x0> <magic 0x543c7af8> <pcomp> <accomp>]
Wed Feb  2 14:32:44 2011 : sent [LCP ConfReq id=0x1 <asyncmap 0x0> <magic 0x543c7af8> <pcomp> <accomp>]
Wed Feb  2 14:32:47 2011 : sent [LCP ConfReq id=0x1 <asyncmap 0x0> <magic 0x543c7af8> <pcomp> <accomp>]
Wed Feb  2 14:32:50 2011 : sent [LCP ConfReq id=0x1 <asyncmap 0x0> <magic 0x543c7af8> <pcomp> <accomp>]
Wed Feb  2 14:32:53 2011 : sent [LCP ConfReq id=0x1 <asyncmap 0x0> <magic 0x543c7af8> <pcomp> <accomp>]
Wed Feb  2 14:32:56 2011 : sent [LCP ConfReq id=0x1 <asyncmap 0x0> <magic 0x543c7af8> <pcomp> <accomp>]
Wed Feb  2 14:32:59 2011 : sent [LCP ConfReq id=0x1 <asyncmap 0x0> <magic 0x543c7af8> <pcomp> <accomp>]
Wed Feb  2 14:33:02 2011 : sent [LCP ConfReq id=0x1 <asyncmap 0x0> <magic 0x543c7af8> <pcomp> <accomp>]
Wed Feb  2 14:33:05 2011 : sent [LCP ConfReq id=0x1 <asyncmap 0x0> <magic 0x543c7af8> <pcomp> <accomp>]
Wed Feb  2 14:33:08 2011 : sent [LCP ConfReq id=0x1 <asyncmap 0x0> <magic 0x543c7af8> <pcomp> <accomp>]
Wed Feb  2 14:33:11 2011 : LCP: timeout sending Config-Requests
Wed Feb  2 14:33:11 2011 : Connection terminated.
Wed Feb  2 14:33:11 2011 : PPTP disconnecting...
Wed Feb  2 14:33:11 2011 : PPTP disconnected

Others can get to the VPN and I can too, but not on my network. The only clue I have seen in other forums is to set the NAT default host on the Time Capsule -- I set this to the IP that my mac got over DHCP.

I made sure that my Mac gets a different range of IP addresses that it would get if it connected to the VPN (192.168.1.x vs. 10.0.0.x).

Not using any VPN client -- just Network System Preferences. It has worked in the past -- but it was a while ago, so I can't pinpoint a change.

My sysadmin doesn't even see incoming connections to the VPN (nothing logged about me when I connect).

Looking for any diagnostic advice at all