For the avatar, when you put it on your profile, did you make sure to change the dimensions to 100x100? If so, try copying the image and putting it on a program such as MS Paint, photoshop, GIMP, etc. and then cropping it down to 100x100. Then just upload to a site such as photobucket or imageshack and use that URL. If that doesn't work, you could either find another image or ask someone who wouldn't mind cropping and uploading it for you. Of course, make sure the image (whether the one you want or a new one) isn't copyrighted.
For the signature, there is a handy tutorial
here where it teaches you how to make your own. You can also find some free ones in
this board, such as
Comitissa's free signatures/avatar sets or
Moonflight's avatar sets.