I used to know of a site that would scan your OS and detect RAM installed, Slots, Maximum Capacity and stick specifications/details so you can go ahead and purchase if desired.
I googled and for some reason could not find what I was looking for. :-
I believe I got the link and info from another Evang. awhile ago. Don’t see him around anymore.
Anyway, any help is appreciated. 
The site I believe is http://www.crucial.com/index.aspx and use the Crucial Memory Advisor™ Tool.
If you purchase from them they have a guarantee that the memory suggested is compatible or it can be returned, etc.
Just awesome guys,
Sorry it took so long to get any replies ;D
LOL Love it when I catch your humour ;D
Seems the older HP LT I just got given to me can handle way more RAM then presently installed. 
Crucial is where I buy all my RAM for myself and my users, I’ve never had a problem.