Ash,

Bettas are one of the very few fish that can live in an uncycled bowl.
(Though they greatly benefit from a cycled tank) Generally, if you want
to have tankmates for your betta, it will require a tank with aeration,
filtration and substrate. I can't stress enough the importance of
researching a species before purchasing it and ALWAYS quarantining new
fish for approx. 4 weeks before mixing them in with healthy fish.
Statistically there is a good chance of exposing your betta to any
number of communicable diseases if your don't first quarantine your new
fish.

Tank cycling and fish quarantining are commonplace in the hobby and all
fish keepers should understand their importance.

Swordtails generally do best in 10 - 20 gallon, cycled aquariums,
heavily planted with lots of light. They need lots of room to swim
around and get to be about 4" when full grown. They are not appropriate
for a 3.5 gallon bowl.

I urge you to return your swordtails and begin researching into the
Nitrogen cycle before choosing any tankmates for your betta. Also, I
have to agree with John, if your betta isn't being active and
interactive, then there may be something wrong. Since your bowl isn't
cycled you should be testing your water several times a week for
ammonia and other toxins as well as pH. Perhaps your fish is being
exposed to the invisible, yet deadly toxins commonly present in tanks
that haven't bet cycled.

To get you on your way, here's some information on the Nitrogen Cycle:
http://www.nippyfish.net/nitrogencycle.html
and choosing tankmates for your betta,
http://www.nippyfish.net/tankmates.html

I'm pretty sure you'll be able to keep your 3.5 gallon bowl and make
things work. It just takes a little careful planning. ;-)