postgresql 7.1, just released, is supposed to be able to get around the 2gbyte limit of ext2fs. I don't have any clue how well it performs in that terrain, having only worked with test databases that big a few time and finding them slow in every dbms there is. Postgresql supports full text indexing, but I have no idea how well it actually works.
I believe Oracle as well can get over the 2 gig file size limit, but can be quite a bit more expensive. It's full text indexing is very fast.
RedHat 7.1 was just released, so you could try testing on that. I don't know if it has reiserfs enabled in the install, but am sure it can bolted on at a later time after the inital install is complete.