Hi There,
Something else you may want to consider is your laptop's inbuilt ethernet card. For my day job I help run a 250 computer network (although normally only around 100-150 of them are active at any one time) using a server with a paired network adapters (2x 1 Gigabit), and recently we had a problem where only one of the network adapters refused to function, so we were stuck with just 1Gbps and because of that the network performance was degraded quite badly. I assume that your laptop has a 1Gbps ethernet card? If so you should be alright with upto 50 clients simultaneously connected, but any more and you will start experiencing serious lag.
As for the version of MS Server to go for, well I use Server 2000 on my network and it works great but unfortunately I don't have any experience with 2003 so I can't offer a comparison. If this is your own laptop I would suggest creating two seperate partitions and having Windows XP in one and whichever version of MS Server in the other. As for having Office installed, that isn't a problem it will work fine with Server 2000 although seeing as you are using a laptop as the server its not advisable to have any applications open that will use up CPU time and RAM, as you'll need all you can get!
Hope this helps