Internet connection sharing issues

I have a Dimension 4400 and a Inspiron 5150 set up on an ad-hoc network.  I recently had to do a complete reinstall of Windows (actually upgraded from XP home to XP Pro) on my Dimension.  Before, my Dimension was my main computer with the Cable connection for the internet running into it and my laptop accessed everything through my desktop (printer, scanner, internet, etc.).  When my Dimension crashed a couple of weeks ago, I switched everything over to my laptop.  Now that I have the Dimension running, and I have the network working (for the most part, I'll touch on that real quick here).  I want to switch back to the Dimension.  Here are my issues with that.  One, like I said before, the network is working OK (file and printer sharing is fine), except for one thing, I cannot access the internet connection on my Dimension through my laptop (which is connected to my modem right now).  I tried the network setup wizard to no avail, and I also adjusted all the settings manually (IP addresses, Internet connection settings, etc) and I still can't get internet access.  Any suggestions?  Did I miss anything?  Also, I am running SP2 on both, but I was before the Dimension crashed with no probs.  If anyone could help, that'd be awesome.

Todd