I've been reading this thread for a little while trying to recall the last time that I did something exactly the same way (regardless of OS). I was looking through spreadsheets and visios of old clients... lol
Guess you had to be here... A N Y W H O.....
First, simply put... this should work with this way you had it setup. If you want to go down the bridge method.. fine, but the original "idea" is fine just the way it is... just needs to be setup correctly.
Think of anything beyond the XP machine to be "The internet" as far as your vista machine is concerned. So, since your XP machine is working just fine.. we will assume that nothing needs to be touched there.
Second, your connection to the internet on the XP machine isn't functional because of the wired Ethernet adapter, it's because of the wireless adapter... The Wireless Adapter is doing all of the work and the Ethernet card should be setup as the "Red-headed step child" that just passes information along... In that sense, treat it with the least amount of respect and give it the least amount of configuarables... What are the least amount of configurables for a network adapter in order to get it to work??? IP and SubMask! (Sorry that I place things along with colorful and needless imagry... thats just the way I like to make this stuff fun) So, on the wired adapter, your IP and subnet mask are needed but your gateway address isn't. I would remove that. The reason that I say this is because of the way that XP and, even more complicated, Vista "decide" how to get on the internet... or choose their gateway. This is ultimately going to force your Vista machine to "say":
Vista Machine: "Hey, how do I get on the internet?"
XP Machine: "Well, what is your gateway address?"
Vista: "192.168.0.1"
XP: "Ok, well I don't have a gateway associated with that address, so let me give you this one"
Then it forces a forward of that gateway address because, according to your XP machine, it's the ONLY way it knows how to get to the internet. I know that it sounds silly and I'm making it sound even more silly... but, you are just asking for trouble when you use addresses in network configurations when they aren't needed.
Last thing that I see that could be a fuss is your vista computer. Is it setup for receiving an IP from the XP machine? Or did you place that address in there as a static address? Personally, let ICS do the work... the more addresses you statically assign, the larger the margin of error could be. If it isn't already, setup the Vista machine to obtain an IP address automatically.
So, in the order that you gave in one of the previous posts, make the following changes:
XP Machine
Wireless Adapter
IP: 192.168.0.138
SM: 255.255.255.0
DG: 192.168.0.100
Ethernet Adapter
IP: 192.168.0.1
SM: 255.255.255.0
DG: Leave Blank
Vista Machine
Dynamic Address
Test out the dynamic address and see what it gets
Post back with the IP, SM, DG and DNS addresses it gets. Should get them all if your XP machine is setup with ICS with the wireless card.