they aren't that bad for a beginner :) In the first one there are 2 white pieces in it, pleas remove it. And add a nice black border. And i think one render is enough in one sig. Also try to the use the bledingoptions the right way. Because the render with the green/yellow backgground doensn't fit.
BUT OVERALL GOOD JOB!
On the second i don't like the border ( i think it's just me:P), i don't really like those techy borders... Fix the text (remove the wind and make it smaller)
Looks around on gfxvoid there are a lot of tutorials in the tutorial section.
It's way too green. The stock on the left is flat and it just doesn't flow with the background. Try to stay away from pixel fonts as your main text. Use something like Arial or Tahoma. Something simple, but nice. 1 pixel borders look better than the 2 pixel border you used, but keep at it. You'll get better. =)