Can a Windows XP Home desktop be made into a WiFi hotspot for using other wireless devices?
We are in a metal building and the DSL modem is in another central room.
Not in the way you would like.
Yes, you can make the Windows XP computer stand out as an Ad-Hoc wireless access point, but it won't be a hotspot. However, the computer would need to be left on all the time.
Now... I want you to really, really think about this. Are you saying that this option is better than purchasing a $30 wireless router you can put next to that Windows XP computer?
Think about it. Wireless router. Typically uses a 12DC adapter drawing 1 amp. So... that's 12 watts. The Windows XP desktop? The power supply alone is most likely drawing 300 or more watts. So, right there, running the Wireless Router is cheaper than leaving the Windows computer on all the time.
Now, since you want to make the XP box a wireless hotspot, you most likely have it connected to the DSL modem via an ethernet cable. Ok. You just need to connect the Wireless Router to the same ethernet cable. No, you don't connect it to the Internet port on the router. You connect the ethernet cable to one of the regular ports. You then set the router to be just an "Access Point". I've got an inexpensive Belkin 54g router sitting here, where you simply "enable" the access point feature, and give it an IP address that you want it to use on your network. It will then take whatever internet signal is available on the network it is connected to, and rebroadcast it over the wireless.
Of course, I'm certain there are details you have left out, certain factors that will give you reason to argue against this simple and time-tested solution... and I'm certain that you will provide those details AFTER I have posted this answer. However, this is still the best solution. Ethernet cable from the modem to the router, and the router in the room where you need the wireless internet access.
I found a guide how to turn a desktop into a wireless hot spot. I am skeptical it would be worth the hassle and expense considering the availability of cost effective wireless broadband routers. It is my opinion it would be much easier to purchase and setup a wireless broadband router connected to your DSL modem. They are very simple and quick to setup.
Here is a link to CNET reviews of these routers. Many are available at department stores and places like Best Buy.
Also, here is a link to CNET's Wireless Buying Guide, which has helpful information.