So I discovered a handy trick on my Powerbook. I tell my DHCP server to assign the same IP to it on the wireless and wired interface, and the Powerbook is happy. I can have streaming music playing while wired or a file transfer, and it doesn't skip a beat if I pull the wire and start roaming wirelessly.

Tried to do the same thing on my XP laptop, and instead of working, I noticed the wireless connection without an IP. Further digging found the wireless connection was asking for an address, but when provided the same one as the wired interface, it balked and requested a new IP. The server and XP went round and round for about 20 attempts, then XP finally gave up. I pulled the wire, and watched as my laptop lost all connectivity until I manually chose to "repair" the connection.

Any ideas if XP is capable of this type of seamless network transition, or is this going to remain another thing my Powerbook does better?

I used to do exactly what you are suggesting with XP and it worked fine. I don't do it any more, but I don't remember having to make any unusual settings when I did have it set that way.

I am at work at the moment but will give it a try at home this afternoon (half day today )

Now I come to think of it there was one difference in my setup.

Though I was using DHCP on the WiFi connection and was using the same IP addresses on both connections, the IP address on the Ethernet connection was manually set rather than using DHCP.