Dell 6400 notebook running really slow!

I bought a Dell 6400 notebook for my brother several weeks ago for his birthday. He has only just got around to really having a go using it and we've found it really quite slow. I'm just wondering if it is being this slow because of the small amount of RAM is has in it, only 512Mb.

By slow I mean that Vista is running pretty damn slow. Just doing something simple like opening a folder containing photos would take a long time to display. I wondered if it could be anything else like a fault somewhere or Vista not being funny working but the small amount of RAM seems the most logical explanation. I've heard several times that Vista requires a lot of RAM but I've also seen that in the recommendations, that 512Mb should run Vista.

Any thoughts? If I were to upgrade the RAM, what would be the best option. Another 512Mb so that it can run in dual-channel? Or something bigger?

I can't remember the exact spec's but it's something like this:
Dell 6400 Notebook
Dual Core
Vista Home Basic
512Mb RAM

Thanks.