more information would be required as there are multiple dell 10" netbooks if i recall correctly
what OS are you using?
windows 7 starter? XP?
how much RAM does your netbook have?
1 GB? 2 GB? 3GB?
for XP 1GB is likely enough, for windows 7 you might benefit from 2GB
the most limiting factor on netbooks is usually the CPU and HDD
i'm guessing your netbook uses an ATOM single-core, which is likely a limiting factor.
many people have replaced their HDD with an SSD to improve snappiness, but only you can decide if that's worth it
note: the dell netbooks tend to only support 1 RAM stick, and it is upgradeable (some of them have 1GB built in i think :S).