What you can do depends on what you have and what you can afford. Most steel bikes before ~1997 are 1". In order to make the swap, you will need these parts at minimum:

- threadless headset
- threadless fork with enough steer tube to extend beyond the headset when installed on the head tube
- necessary spacers, top cap and starnut, OR compression plug/top cap.
- threadless stem that stem that is the same size as your fork steer tube on one end, the right bar clamp size on the other, and the correct length/angle for your fit needs.

When you change from threaded to threadless you are basically changing a whole system. It's important to keep in mind that the type/quality of fork you use can and does impact the ride and sometimes the handling characteristics of the bike. Many people say that the fork can account for about 50% of the bike's feel (I would tend to agree). This something to keep in mind when doing your research on what fork to get.

Since you said you are considering a carbon fork, it's probably worth noting that full carbon forks are usually better than CF with an aluminum or steel steer tube. They are lighter, often ride better and are usually stronger as well. The downside to this is that, while a carbon fork is usually better, you there is an inherently smaller margin of error in the installation process. I'd wager that about 90% of carbon parts failures not resulting from crash are probably from using incompatible parts and improper installation. One thing to be especially careful about is stem selection. Some stems are poorly designed and tend to slightly crush things as they clamp down. Another thing is, a lot of inexpensive stems have poorly machined parts that don't sit flush when installed, don't tighten uniformly, or have sharp edges that can cut into your fork or bar. The best remedy for this is to do your research and find out what's compatible. Well designed and installed carbon fiber parts are very unlikely to break in normal use.