Have a look in FAQ section on the main page
If you're still having problems/unsure
Go and download windows XP power toys picture resizer.Its on the microsoft website.
This is the quickest easiest way to resize them for this site[small,med,large all upload without problem]
When you post-click add an attachment ->then browse to the folder you normally keep your pics in->right click on the pic you want and resize it
[this depends on you having downloaded the powertoys resizer first]
Best if you resize first then click add attachment,find the pic ->d/click it,then click add attachment again[not the add button above browse the one below]
Any further issues post up another query
If you dont run XP,then im sure they do the resizer for vista too
You might also find some instructions on youtube for this kind of thing :?