Yes, u can.
However, because you are now entering the realms of multi-tracking, u would need the recording software to match.
I.e.. Wavelad (Cubase) can only record two tracks (mono) and will not see both soundcards simultaneously.
U need to get something like Cakewalk or Cubase. These packages will see both soundcards and you can then record on both.
Another idea is to get two adapter plugs that will split the stereo input of the card (assuming u are using something like a SoundBlaster Live) into two mono inputs, which you can track seperately. This will, with two sound cards, give you the ability to record to 4 mono tracks.
Warning: If you use two dissimilar cards, you may get problems with different lags. This depends on the performance of the sound cards. Cubase does give u some control over this and u may be able to make it work.
Good Luck