Wow, I haven't seen an old HP Pavilion 6000 series computer in a good long time! Your going to be a little hard pressed when going to your local computer store and trying to buy a stick of RAM for this thing. Man, a 6600 running Windows 95, I haven't seen a computer run Windows 95 in eons. Well I'll try my best to snap out of my little "shock and ahhhh" thing and get back to talking about the RAM.
Again, going to your local computer store might be pointless, most likely they aren't going to have anything for you. But by happens chance I took the liberty in doing a bit of searching on-line for a supplier that still provides RAM for the old HP Pavilion 6000 series. Give the following place a look...
Arch Memory Store
http://www.archmemory.com/ram.cfm/H...y-RAM-for-HP-Pavilion-6600-Series-23118-63607
Now seeing what I saw on that web site made me shake my head and think to myself that upgrading this old dinosaur of yours might not be worth it. This web site only provides 3 different memory sizes for your computer. (1) 32MB's, (2) 64MB's and last (3) 128MB's of memory! I'd hate to hear what your system currently has as far as the amount of memory it has. With a bare minimum of 64MB's of RAM your system will run really bare bones and "no thrills" with something like Windows 2000 Professional! Your going to have to pump it up a notch and maybe try for 128MB's of RAM, if you want to install and run things, again at pretty much "no thrills" with something like Windows XP. But with Operating Systems like Windows Vista, Windows 7 and the up and coming Windows 8, I don't care how much RAM you try to squeeze into that old computer, it isn't going to be close to enough.
Again, if I'm on the mark here and truly found your computer and this is the one, I would again think twice about upgrading it! Plus with it running Windows 95, finding product support for that via the web is going to be impossible, Microsoft stopped providing support for that product 17 years ago.
I'll shut up now, just due to bafflement alone, I can't stop rambling about this!
Good luck.....
**Zen exits the room, shaking his head with a baffled look upon his face**