If shopping EBAY or the ads, what laptops are user friendly,upgradeable, etc. Looking for an older model, under 500mhz.

How much do you want to spend?

With the exception of bringing RAM to Max and maybe a bigger HDD, most laptops are not upgradable. IMHO

There are few parts of a laptop that are 'upgradeable'.
The 'use of quotation marks' is because there are many things in a laptop that can be upgraded - but it isn't easy (I haven't ventured there myself!) in theory, there is a lot inside a laptop that could be upgraded -hdd, even the proc in some cases, but it means taking the laptop to bits - not something to be taken light-heartedly.

Some laptops do allow for easy upgrade - My Acer allows me to change hdd, dvd etc, but the problem then arises of cost and availability - be aware that everything you could replace will come from the laptop manufacturer, and they control the prices. Older replacement parts may not be readily available, and you could certainly expect to pay a premium for any parts.

Some manufacturers are now waking up with laptops and even making thigns like graphics cards replaceable (fuzzy head prevents direct recollection of specific manufacturer:D )

Another thing to think of with used laptops is battery life. The battery is the one part which IS going to fail - check whether you can find suitable replacements before looking at older models.

It may well be worthwhile looking for end of line new laptops rather than older, secondhand ones.