In looking at the boards this morning I couldn't help but notice three posts from you all having to do with more or less the same thing. Besides the fact that they really belong in the Networking Forum, am I correct in thinking that it's all one and the same and that this particular post does the best job of explaining what you have and what you are trying to do?
OK, I'm thinking that if you're bound and determined to make the XP desktop act as the go-between wirelessly for the laptop, what you're going to need to examine is each wireless adapter's software for the "ad-hoc" settings and get those in order. I don't think that Windows will give you this control so you may need to dig out the CD that came with each computer for the wireless adapter software (note: not same as the driver). But with ad hoc you should be able to get the two devices talking to each other.
Now in order to share a network/internet connection out to the laptop, you'll need to employ Internet Connection Sharing (ICS) on the XP Pro desktop.
That being said, I'm not sure how the server is going to react to the laptop yet; at a minimum you may need to administer it (the server) to see the new machine by entering it's name but it's been a long long time since I've had my hands on NT4 and that may only apply to Active Directory type servers anyways.
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OK, now ALL THAT being said, you'll really be much better off by buying a wireless router and putting that in after the broadband modem, then the laptop can connect directly to the network wirelessly through it and you can avoid the whole ad hoc and ICS business (which I'm not 100% sure will work given the laptop is XP Home ed. etc.).
Hope this helps.