I'm in the same position. Tuner cards seem to be very picky and need a very clean, strong signal to get reception, much less a good picture (much stronger that your average tv).
I have these cards and it has been the same with all.
One thing that seemed to help a little was to let a vcr tune the channel and let it send the signal to the card via composite. In all honesty, a good outdoor antena is your best bet. IF that is not an option (its not for me as I am in an apartment), plan on doing a lot of homework to find a good indoor antena (I'm guessing you are not in a strong signal area as you are only getting two channels). The problem with indoor antenas is that there is no perfect antenna. One that works good in one area will work crappy in another area (been doing some research on it). Most of the cheaper amplified antenas like you would find at walmart are total crap. I have a couple of them and none of them work well (and reviews say the same). There are actually sites dedicated to tv reception and such if you search. I have an old terk amplified antenna that actually works very well, though wouldn't you know it, the channel that I most want to be able to record, comes in but with a crappy picture.
If you have cable, it might very well be worth running some coax cable to get a signal off it, even if you are going from one room to another. Otherwise, its an outdoor antenna or go hunting for a good indoor antenna. Believe it or not, radio shack is a good place to look. My last atempt at this will be with a pinacle studio av/dv capture card (no tuner, I'll let a vcr do the tuning as it seems to work beter and I have spare vcr's)
this radio shack antenna (it has some very good reviews but again, what works in one area wont in another)
It was recentlly discontinued but I found a store that had one (50$).
If that doesn't work, it's cable or I give up.....