The avatar dimensions are slightly different. You will most likely have to resize to upload. The requirements for the avatar is on the page where you will hit browse to upload your avatar.
The signature is quite different. It took me a while to figure it out. You have to save an image that you want to use as your siggy, and load it. You have to use a certain vb code. I didn't realize this, but at the bottom of these pages, is a list of posting rules, so, after you upload your siggy, you can click on the vbcode and it will show you what codes to use to do whatever. In the signature use the vbcode , you have to copy and paste the url for your pic after it is uploaded, you will see it after it is uploaded. anyway, this has to be typed in the big empy box in order for it to appear in your posts.
hope this helps. any more questions, feel free to pm me, or Poirot, or Wayne.
Everytime I type in the vbcode, it disappears, but, you put your bracket([) then type in sigpic then another bracket (]), type in the url that you copy and pasted, then bracket ([) then type in /sigpic then bracket, with no spaces.