Call an Electrician.

You need a double 15amp breaker. Since you don't have any empty slots you need to have a sub panel installed. You can't use the existing 15 & 20 amp breakers for this application.

seeings how I have a single 15 amp, cant I replace it with a dual 15 amp breaker w/0 installing a sub panel?

NO you can't use a tandem breaker for this aplication. It only pprovides 2 120 volts circuits. You need 2 full spaces in the panel to get 220 volts.

What if I used 2 tandem breakers. One to consildate 2 15 amp breakers and 1 to run the 220?

I have ample 15 amp single breakers

http://www.pwctoday.com/download.php?id=21223

this is a picture of my box

they make, at least for some panels, a tandem dual breaker where either one or both sets of breakers are tied together. ( 2 inside breaker handles with a bar connecting them together for 220 and a similar arrangement for the outer two. I have also seem them where only 1 pair are connected for 220)