Ad hoc network connection problems, XP to Vista

I'm trying to set up an ad hoc network between an IBM T43 running Win XP Pro
SP3 and a newer Dell laptop using Vista SP1. I can define the ad hoc
network on the XP and get the Vista machine to "connect" to this network.
But the T43 will not connect. I have selected "Use Windows to configure
settings" in the Wireless Network Connection Properties window, but IBM
Access keeps jumping back in and takes over. I think I might get farther if
I could work only in Windows without this third party program making my
waters muddy. Funny that even tho I used the ThinkPad to create the network
it is the machine that is having connection difficulties.
Any thoughts on how to get this set up?
What differences between XP & Vista in this matter do I need to address?
I'm sure some things have changed.