What should I know when looking to buying an external hard drive?

I use a Compaq Presario VP2000 laptop, and am currently using 41 of the available 74.5GB, most of it media (video, music, etc...). My laptop has been doing pretty well for how bogged down I keep it, but I know the only thing keeping it from top performance is the fact that I have all of this on the main drive. I plan on keeping the hard drive in one central place if I can, so I'd be keeping all the important things on the C drive.

Special issues: I live in Las Vegas and it gets hot here. Easily 120F in the Summer. Will cooling be an issue?

Are there any brands that are better than others (and reasons just so I avoid fan-boy/girl-ism)?

What are some problems I can expect to encounter?

What price range should I be prepared for?

Will my anti-virus (AVG) be able to scan the hard drive?

What should I know when looking to buying an external hard drive?firewall

The best advice I can give you regarding external enclosures is to make certain that they come with an on-board cooling fan. About a year ago I bought an all-aluminum enclosure off of NewEgg and put a 160GB IDE drive in it. The drive worked fine for some time since I'd only bring it online to do backups. A short time afterward I started using keeping it online for longer stretches.

The aluminum was meant to radiate the heat of the drive but, and I'm sure you know where this is headed, it failed to do so. Shortly thereafter I had a failure with the disk media and had to get the drive replaced (thankfully it was backed up).