I don't know if you have ever kept bettas before, so I am writing this post like I would to someone who never has. I have only been keeping bettas for 8 months, but by gleaning knowledge from this site almost every night of the week, I have learned more then I ever would have imagined about these awesome fish. If anyone here sees anything wrong with anything that I type in this post, correct me. My opinion is that every time I make a mistake, I learn more. Oh, and I'm afraid this might get a little long. Sorry in advance!
Anyway....... to get to the point.....
I have used an adjustable temp. 25w heater in a 1 gal bowl with success after days of testing (without a betta in there) just to get the temp right, and 3 days more just to make sure it stayed the same after I got the temp where I wanted it, and it worked like a charm. You will just have to turn the temp way down and adjust it up a little at a time. You will want a thermometer (a floating thermometer is the most accurate) in the tank so you can keep an eye on the temp.
Keep in mind with an under gravel filter, you will not want to over clean your gravel as this is the filter media and over cleaning will disturb and/or kill any benificial bacteria that has begun growing there. That and under gravel filters usually cause a lot of surfact movement from the bubbles rising up through the tower (unless you use a gang valve to reduce the air flow), and bettas don't like a lot of surface movement. A lot of people, including myself, don't like to use undergravel filters just for those reasons. A lot of us don't use a filter at all in 1 gal tanks, and do a 50% water change halfway through the week, and a 100% water change at the end of the week to keep the ammonia levels down. Filtering in an uncycled 1 gallon tank won't help at all in keeping the ammonia down unless it's cycled, and cycling a 1 gal and keeping it steady is usually harder than in a bigger tank so you might be better off going without the ufg. I see in your profile that you have a 25 gal so you should know about cycling.
Have you read over the pinned topic "Betta Basics" yet? If not you might want to look over that as it contains a lot of very good information in keeping your betta happy and healthy.
If you don't have a test kit, get one that tests for ammonia, nitrItes, and nitrAtes so you can keep an eye on those levels every other day to keep your betta healthy. If you decide to ditch the under gravel filter, all you will really need is a test kit for ammnoia as that is all that should show up in an uncycled tank that gets regular water changes.
When you do water changes you have to ensure that the water that you are changing it with is no more than a couple degrees off of that which is already in the tank. This will cause major stress on your new betta buddie and may cause him to devolep a disease of some kind. But like I said before, you have another tank so you should know this already. An idea here is to keep a bucket of conditioned water (if you have room for it in your office) with a heater in it and try to match the temp as closly as possible for water changes.
Feed your new betta buddie a virety of foods, and try to stay away from those color enhanceing foods cause sometimes they are not always that great for them. Freeze dried foods aren't too great for them as most of the time they are pretty hard and can tear up their insides. One of their favorites is blood worms. You can get frozen blood worms at most fish stores. They like brine shrimp as well, but they are mostly water so they aren't really that great for a regular diet.
I feed all my bettas 6 pellets once a day, frozen blood worms once a week, frozen brine shrimp once a week, and fast them 1 day a week. I try to feed them a pea at least once a week. It's good prevention for constapation.
Anyway, I think this post has gotten long enough so I am going to end it (if you have not gotten bored by now and quit reading) in saying good luck with your new betta buddie!!! Hope this helps! Really sorry for the long post! I just want the best for any betta out there.
. For Christmas he purchased a 1-gallon tank for me with the intentions that I get a betta and keep it on my desk at work.
I don't want to make the same mistakes i made when I fist set up my initial tank so any advice I can get now is good! So sounds like I might not use the UGF and just do more water changes. I do have one more question though about that. How do you do a 100% change without completely stressing the betta out? 
