Unfortunately it is not a small screws, but a some kind of stamped screws - not removable. I actually don't remember any Dells with motherboard side panel been removable.
So, you have to take out motherboard.
Are you planning to change CPU cooler?
Which model you are planning to use, generally Dell adopted LGA775 size (for CPU cooler) for a lot of its motherboards, yours might be included, so you know.
Dell backplate is usually glued to motherboard and not easily removable, so I will give you a link to my Inspiron 570 upgrade guide. If your motherboard appears to be glued, use my guide to remove backplate.
In the following link scroll down almost to the middle and after talk about cooling you will see the procedure describing backplate removal
http://en.community.dell.com/support-forums/desktop/f/3514/t/19490818
Good luck.