I don't really come from a tech-savy family. My brother-in-law got me started and I just taught myself from there.
It's not like building a computer is hard, if this doesn't fit, then put it somewhere where it will. I've done a good bit of online computer builds, they're not as easy or fun but they are possible. If you have no knowledge at all of a computer's hardware, I suggest you either study how to put one together or goto a friend and have them build it due to the possibility of simple mistakes (such as not grounding yourself to the case.)
Now as for laptops, you don't really build those but I bought one from Toshiba for about $800 and it plays Blockland better than my Desktop does.
Intel Core i5 M460 @ 2.53 GHz
4 GB of RAM
ATI Radeon HD 5650
This runs relatively well in anything I put it through, of course the mobile stuff is never as powerful as the desktop stuff but that's expected. I bought this around Christmas of 2010 so there are a lot of options that you could consider that would be better than this laptop specifically.
http://www.newegg.com/Product/Product.aspx?Item=N82E16834214418This one has a little bit of an underclocked processor compared to mine but it is a Toshiba and mine has been good to me for 7 months so far.
The RAM, GPU (Graphics Card), and HDD's are bigger and better than mine though.