I have a humor blog and need software that will edit photos (change heads etc) and write on a photo (like hand drawn arrows and comments) but I don't want to spend $600 on Photoshop: are there cheaper alternatives?
As already mentioned GIMP is totally free and (in my opinion) very very good. Will certainly do what you say you require (chopping off heads, arrows etc), get it at:
Then get take the money you have just saved and buy your first tablet, as this will have a big effect on how you work (at least it did for me). GIMP + Tablet should allow you do do pretty much most things easily.