Works fine with my ADSL and dont see why it shouldnt work worth dialup as long as there is sufficiant bandwidth to make the game palyable without too much lag.
All you do is plug your xbobx into the hub or switch on your lan, run the game you want to play on the xbox and the run the program on the machine that you have a connection to the internet on.
The program picks up up the IP of your internet connection. It then searches your LAN to find XBOX's that are attached. You then choose what game you want to play and if you want to host or join. It also gives you a chat window so you can see if theres anyone looking for players etc.
If you dont have a network set up it might be worth trying it with a cheap network card in your PC and a cross over cable to the x-box. I see no reason why it shouldnt work that way too.
At the moment its seems that Halo is quite fussy about what other versions of Halo it connects to. Certainly PAL will only connect to PAL and NTSC to NTSC but some users have reported that french PAL will not connect to UK PAL games etc.
When I tried it certainly seemed to be the case. Maybe future versions of the software will be able to intercept the X-Box net packets and do a translation to allow users to select which country they want to 'look like'. This in conjunction with the PAL/NTSC selector disk would mean that all users can play against eash other which surely is the whole point.
Lets hope so, good luck and post your results.
