For the last couple months, I have been building small HTPCs with a variety of software on them, tailored to what my customers (so far just my friends) want.
There is a market there, but I'm wondering, I'm just installing open source items such as XBMC.
Is simply providing support in exchange for money for open source apps legal? People who work off the code have to release their work to the community.
It would depend on what the license said exactly because not all open source is the same, but that being said, I've never heard of any open source license that would prohibit providing support for money.
You could even sell the software (under most open source licenses) if you want as long as you let the consumer know that it's freely available along with the source code (now why they'd want to buy it knowing that is up to you. In your case you're installing and supporting it which is definitely one way to go)
First of all, there is a difference between releasing your code to the community, and releasing your code to the customer. Check your license. It may very well be the case that you are only required to provide the code to the customer who may not want to release it to a third party. It looks like XBMC is free software, though I recommend you not rely on that until we are sure we are talking about the same thing. If XBMC is free software, your obligations are defined by the GPL.
Generally, if your software is free, the issue is freedom not price. So while you have an on-going obligation to provide the source, you may always charge whatever you like.
I am extremely familiar with this particular license, and am happy to take questions off-line (website below).