OsCommerce is great if you know a bit about PHP modding, but it's pretty bare if you install it without any mods.
A friend of mine uses ASPcart for this sort of thing.
There's another one I looked into a while back when I was thinking of running an online shop. I'll look into the name of it tonight.
But yeah, it was basically a thing where you'd upload it to the admin section of your site, make sure SQL access was on, and then go to its install page. It'd basically ask you what features you wanted installed, and then do it all and tell you to come back in 30 minutes.
Then it was just a matter of making product categories, and uploading pics, descriptions and prices. Would take a while if you had heaps of stock, but yeah, totally user friendly.