Bruce kind of side-stepped your questions there...
I have a really old soundcard with a midi output...
Do you also have a really old computer, or a really new one? Few motherboards are still made with slots that would accommodate an old soundcard (the so-called ISA slot). So depending on what you mean by "really old" and how that relates to your computer too, maybe you can use the old card and maybe you can't.
If you can physically get it into your computer, then yes, it
should work. (I say
should work because there is always the possibility that you might have a resource conflict that you cannot resolve between the old and possibly inflexible soundcard -- some of which are hard-wired to use only a certain IRQ and some fixed ranges of memory addresses-- and the other devices already installed and cooperating peacefully in your computer.)
If you do have a newer PC with PCI slots and no ISA slots and the "really old" soundcard is indeed and ISA card, then you're stuck. There are several models of MIDI interfaces available, some of which connect to the PC through standard ports like USB, serial, and parallel. That would probably be your best bet.
I was wondering if I could use that and then set the sequencer software to use the sounds from the keyboard instead of the soundcard...does that make sense??can I do that??
Absolutely, that is the whole reason such a thing as a MIDI interface exists. The MIDI interface of the card sends and receives MIDI messages to and from external devices like your keyboard. That's what its for. You are
not limited to playing your MIDI tracks from the soundcard's own MIDI synth. All you need to do is select the right destination for the MIDI data in your tracks -- the MIDI Out port and not the card's synth. Then, assuming the cabling is correct and the keyboard is set to recieve the messages the way you want, you'll get the keyboard sounds.
and will there still be bad audio quality if the sound card is that old??I just need the sound card to connect my keyboard to the pc...
The audio quality of the old soundcard will have absolutely nothing, zero effect, on your intended purpose.
P.S. The fact that you even ask this question leads me to suspect that you don't have a clear notion of what MIDI data actually
is and what it's for, so I suggest you read up a bit on it before you start trying to make use of it or you'll tie your brain in knots.