RAM - HP LAPTOP

It supports a maximum of 1GB using 2 512mb modules.  You most likely have one 512mb and one 256mb module (the difference is being used by the video system).  You can replace the 256mb module with a 512mb module to max out your memory.

Yes, I just added 512mb. Do you think it is the best way to go to upgrade this model?

I actually doubt you'd notice a significant difference between what you have and 1GB.   If you're looking to make the system "feel" faster, you'd probably be better off replacing the hard drive with a 7200rpm laptop drive -- you could bump up the size while you're at it.

It really is the only easy way to go in terms of upgrading unless your comfortable with taking apart your laptop.  Generally laptops are much trickier to disassemble than a desktop.  I think you made the right choice in upgrading the memory.

Yeah -- for about  $45.

Newegg has some good prices on 200 pin SO-DIMM's

http://www.newegg.com/Product/ProductList.asp?N=2010170381+1052907864+1309121111&Submit=ENE&SubCategory=381

hard drive with a 7200rpm laptop drive? Does it matter much about the size 80G, 100G, etc?

... two different questions:  

(1) WAS it a good idea to add 512mb -- ABSOLUTELY

(2)  IS it a good idea to add more (beyond 768MB) -- Not so clear;  as I noted above, the incremental difference in performance is likely to not be noticeable (measurable? - Yes;  perceptible? - probably not).    If he's looking for a "faster feel", getting a high speed hard drive is much more likely to provide that than more memory at this stage.

"... Does it matter much about the size 80G, 100G, etc? " ==>  No; just buy whatever size you'd like to have :-)

Excellent advises. I added more points... up to five hundread. Thank you