Actually, SG-1 was aboard an Asgard ship that was crawling with replicators. There was no way off the ship and the only way they could think to prevent the replicators from infesting the planet was to wait until the ship was entering the atmosphere and knock out the engines in oder to make the ship burn up in the atmosphere. What they decided to do to survive was to beam the stargate up to th ship, dial out to another planet and then return once the SGC got the second gate operational. This was in season three's finale Nemesis. They search for the gate in the ocean, where the Asgard ship crashed, and didn't find it, so now there was only one known gate on Earth. In season 4's episode Watergate, they find that the Russians found the gate in the ocean and started up their own gate program. The ate got stuck open and they couldn't figure out how to get it close so SG1 is sent to fix it, of course. After that the Russians decide not to run their own program any longer. In the premier of season 6, Redemption, Anubis uses a piece of Ancient technology to destroy the SGCs gate. The Russians offer to let the US use theirs but are initially turned down as Anubis could do the same thing to that gate. Meanwhile, Teal'cs son Rya'c destroys the Ancient device and that lets the US take the Russians up on their offer.
Can you tell I have the first 6 seasons on DVD?
You can also go to Gateworld.net to look this stuff up. It is a really well done, and large, fan site that has all kinds of resources you will probably like.
http://www.gateworld.net/index.shtml