I'm currently working on this site:

http://webs.ath.cx:8000/users/flyertrade/index.php

I want to buy a domain for it to make it easier on others.
1) How can I point a domain to this site, even though it has subfolders?
2) Which company should I register with?
3) Can the :8000 be avoided in the domain?

Thanks

You need to look into it a little more. When you register a domain, you point to where the site is. If you do it correctly, you aren't "redirecting" anything persay. You'll type in the domain and it will go to where ever you said your site was. You won't see the url you posted above anywhere.

I like godaddy myself.

You could do a simple thing if you register that domain. You could register and just create a basic index home page with a meta refresh that would re-direct you to that other site. You could also use some php functions (if the server supported it) to include the other content, but that is going ahead.

The other question about the port (:8000), depends on your ISP. Your webserver is listening on port 8000 (usually when ISP's block 80), so if your ISP allows it, you can just change your webserver to listen on the default port 80, restart and no longer need :8000.

Regards.
Lr

1) You would buy a domain at one of the registrars
2) GoDaddy works well for me
3) That depends. If you pay to have domain hosting somewhere (godaddy, cybrhost, aplus, or whatever) and move your site there, then sure, no 8000, no sub directories.

What it looks like you're doing presently is hosting the domain on your machine or under your isps personal web space where the web server is running on port 8000. You could redirect from your domain page to your webs.ath.cx:8000/users/flyertrade/index.php site, but that url will still be visible in the end.

If you have another server with apache on it you can use mod_proxy to mask the port 8000