You didn't give any information on what you were trying to achieve, and what, if any, problems you currently have.
For a basic HTPC, I wouldn't really recommend either, if you aren't gaming or using the HTPC for ripping/encoding. You are fine with 2GB of memory. Are you trying to run Photoshop while watching HD movies? What would you be using the extra memory for? As for the SSD, it improves start up times. How often are you resetting the HTPC? I guess it can be a slight improvement if you watch live TV a lot, and use the PC sleep function to turn it on and off, and you are impatient (do seconds matter to you?)
But if you are on a budget, I don't see either upgrade necessary or even worth the money. If you explained why you wanted to upgrade, what you were trying to achieve, and what, if any problems you have with your current setup (you can tell us the specs if you want), we could probably give you better upgrade advice.