Is memeory specific to each make of computer? (Copmpaq / HP swap)

I realize this is an easy question for anybody who posts to this
group, but I'm a little slow :) My mother in law gave my two year old
a presario 4160 to play around on (hard drive has been formated and it
is running windows 98) but it only has 24 MB of RAM (not enough to
play his Winnie the Pooh game) I need to upgrade this and I have an HP
Vectra I bought from work that never even worked for me and I was
wondering if I could swap the memory from the HP into the Compaq. If
not is there anything I need to look for when buying RAM for the
Presario 4160? Also how difficult is it to install, I imagine its just
plug and run.
Thank you for your help.
Mike