I agree with AJ on this, developing something in-house will not provide you the flexibility and functionality of a commercial tool.
As you may have found out, there are several freeware items out there. I myself have been searching around for a defect tracking tool that is either free or relatively inexpensive given the budgetary constraints of the group I'm working with. I started with the link, http://www.aptest.com/index2.html?resources2.html, and went off from there.
As for MS Access based, check out http://www.pb-sys.com, they have a freeware defect tracking tool called Buggit.
Buggit has pre-defined database tables and fields, but also provides the capability to add some custom fields.
I would say though, don't expect performance to be all that grand with MS Access, especially if you're going multi-user on a defect database. For performance you are better off looking at the relational databases such as Oracle or MySQL.
In fact, I found another freeware tool, Request Tracker (RT), http://www.fsck.com/projects/rt/, which I'm looking to evaluate in the future.
This tool requires you to separately download MySQL and, I believe Perl, though I haven't gone through the specifics of setting up this tool yet.
BTW, MySQL and Perl are both open source and available free for download. Check out http://www.mysql.com/ and http://www.perl.com/