Ok, thanks for the tip. Erm.... im not sure if there is a way to have them both enabled and working, in fact im pretty sure its impossible, but seriously are you 100% sure that your soundcard doesnt have a kline in ocket, not even a microphone jack.....??
If it doesnt then there are cheap sound cards like £10 (USD $20), take a look on ebay, they are fairly decent for the price and if you get a 5 channel card it will have EVERYTHING that you need, of course there sis always the full sound card maret, like sound blasters audigy rand or even something in the £30 range from people like philips or SONY.
CONSIDER UPGRADING........!!!