Wait... Let me get this strait... You have:
Computer w/ ethernet card --> DSL Modem --> Internet
Yes? You may have to do PPPoE through the modem, but I *think* redhat lets you do it. I've got my box going through my modem too, so it's not too tough. You may also have to add another small piece to the puzzle. You cat get a DSL Router/firewall (I really like Linksys for this!) and have THAT do the PPPoE. You can then tell it to route all traffic on subnet 10.0.0.x and set your IP on your linux box to 10.0.0.2 (and the IP on the router to 10.0.0.1). This give you the power of a hardware firewall. I REALLY recommend this, as RH is going to be dropping support for 9 in um, I dunno a few hours now.
Anyway, that's my recommendation. You can also set the FW to forward traffic on certain ports to the box on the other side too, so you can even run a web server, etc through it. Let me know if you want more info than that.