Either get PS illegally or download GIMP, which is sort of similar but free.
I guess the key thing would be to keep in mind foregrounds and backgrounds. You don't want either of them to be too cluttered and you don't want them fighting for attention either. In the sigs you posted it's hard to differentiate between what's supposed to be in the foreground and what's supposed to be in the background, they all kinda blend together.
Simple is really the best way to go when you're just starting out, don't go nuts with effects and filters until you kinda know how to utilize them properly.
There's loads of good tutorials online for various things, like if you have something in mind you'd like to execute there's almost guaranteed to be a tutorial online somewhere about how to do it.
http://www.good-tutorials.com
http://www.dafont.com
Are worth checking out. For tutorials and fonts respectively. The good thing about the sigs you posted is that they are not cluttered. A lot of people new to any kinda graphical thing will try to fit too many aspects into one picture, so I think if you work at it you'll be able to produce some decent ones since you're not trying to pack too much into them.
