Buying an external harddrive would be good, but can you tell the ram of your laptop too?
Low harddrive space slows computers, but it is also caused by overloaded registry. And you shouldn't erase your computer's registry unless you exactly know what you are doing. As of external harddrive, Kingston is one of the best brands around. You can also try smartdisk. How much spare money do you have for it? If you have enough, I suggest you to buy a big one so you can use it for a long time

30gb should be enough. Which operating system do you use and what are your RAM memory and processor?

you can get a 1TB (=1024GB) for 150 USD now I think. Your computer memory should be upgradeable too I think.

Go to Tigerdirect.com. They have loads of merchandise for probably the lowest prices you'll ever find. I just bought a 500 GB external harddrive for only $69.99. Just go to Tigerdirect.com ->(Side Panel) Harddrives. In the descriptions make sure it says "External Harddrive" and make sure it has a case on it on the picture.

get a 2 tb hard disk, that way your bound to have enough to store your data on

Sorry, to freaking lazy to read the whole thread (2 pages!!) I'm not the best hardware guy (I'm the simple question guy on a tech forum)...
What kind of HDD are you after? I head there is some with USB and SATA support. That'd be really really nice. How many computers do you have? What kind of programs do you run? Do you have sufficient ram (No, you have less than a gig of ram)? How much disk space is free? How much disk space is possible?

At the same time? Ouch. No wonder your computer lags. How is your HDD partitioned? How much space in C:\ how much in D:\? If you have a partition of 32 GB in C:\ (Assuming acer auto installs to that) and it's full, then that's another reason. Firefox is a memory leecher. This is one of the times I WOULD recommend IE because it's lighter on resources. Do upgrade your ram and use Firefox though. Also, looking at Windows LiveOne Care on google.. it doesn't look helpful. Common tech knowledge states that best free anti-viruses (in order of my preference): Avast!, Avira, AVG.

*laughs quietly on the side* Windoze...

What's funny is that the ONLY thing labeled "Microsoft" or "Windows" that runs properly on my computer is Windows Live Messenger. I did some Microsoft updates and it freaking crashed my startup. What the hell are you releasing, Microsoft?

Again though, you need more RAM. Your computer can barely handle your OS.

Are they going to charge you? Nah, I'd go to a friend (I could recommend people, but you probably live at least 400 miles away.