Quill stems and Threadless stems are different. There are both fixed and adjustable versions of each.

A Quill stem is smaller in diameter and slides inside your larger diameter, hollow headset:



Photo above is a fixed quill stem. It uses a wedge at the bottom to "jam" it into place and lock its height and orientation.

This is an adjustable quill stem, showing the wedge at the bottom which is common to both fixed and adjustable types:




A threadless stem has a larger diameter clamp that just clamps around the upper part of your headset, it does not slide inside:



Photo above is a fixed threadless stem.

Here is an adjustable threadless stem:



From those pics you should be able to determine which type you have. In either case, you can replace a fixed stem with an adjustable type on any bike.

Your 2010 Sirrus Sport has a fixed threadless stem. You can use any brand or model of stem like in the last picture above to convert it, no problem.

If you wanted to gain a bit more height, this particular brand that you can buy from vendors on eBay has a riser built into its clamp to give you an extra 1.25" height right off the bat, without even adjusting it yet. You should be able to tell the difference between the "standard" adjustable type above and the clamp on this one:



Finally, if you have a quill stem and want to use threadless stems on it instead, you can get a quill to threadless adapter from Jenson and other vendors (you don't need that with you Sirrus, but if you had an older bike with a quill and wanted to convert it this is the ticket):

http://www.jensonusa.com/Dimension-Quill-Stem-Adaptor



That's about as comprehensive a guide to stems as I can make...

Cheers
TRJB