What I currently have:
http://www.dell.com/content/products/pr ... l=en&s=dfh
Dell Dimension E520

What I'm going to get:
http://www.shopping.hp.com/webapp/shopp ... v3z_series
HP Pavilion dv3z series

uh you could get a much better computer for 700 bucks.

That's just the base laptop. I'm customizing it to be MUCH much better. And under $1000.

You're never gonna get the same value out of a laptop as you would for a desktop.

Yeah, if your going to do ANY gaming at all, get a desktop. Just get a inexpensive laptop for portability. Gaming on a laptop is like a joke. Really.

Seeing how the only gaming I do is Cortex Command and occasionally firing up Spore, I don't see a problem with that. And the specs of the laptop will be more than able to handle a game if need be.

Hmmm.... ok lets take a look at that HP Laptop. Processor, old AMD dual core, its outdated even now, not even thinking about what it will be in year or so. Gfx card, old, poor and on top of it is mobile version with even less power, yay. 13,3" display, oh wow so small, years ago when I had my first PC with "powerful" 40Mhz Cyrix CPU I had bigger monitor than that (as a matter of fact it was 14" ,standard 4:3 aspect monitor, maybe this 0,7" difference doesn't seem to be much but take in consideration that this laptop screen is in fact widescreen so you get less for every inch ). Surely it will run CC but other than that not much. Future prospects are terrible, no room for upgrade and its components are already old and as other people said its mobility aspect is overrated, battery will last for 2 hours or so, depends. Mobility aspect you get with laptop is ability to easly transport it from external power source to external power source (can't find that word in dictionary ). Unless you need it for work or something to carry it from place to place its not worth buying at all. Desktops are so much better and cheaper.

Hm..
Might keep that in mind.

Would you mind doing that same thing for what I currently have? (Dimension E520)

So about your Dell 520. Hmm... my PC is 4 years old and not that far behind, also it costed me less. But you have three things going for you. I don't have: Pci Express slot, Dual Core processor, and from what I see its 775 socket board so this means you can go for newer processor. There is room for upgrade here, new processor, E7400 with custom cooling (nothing fancy, just not that fan which comes with it in box, buy OEM version instead) and little bit of overclocking would be fine, if you feel rich you can go for quad core, buy video card, what you have right now is utter cr*p, my old 7600GT is so much better and its poor at best and on pci express you have what to choose from unlike me stuck with AGP and higher prices for less, new GTS 250 512Mb (1GB version is waste of money, it does better only in ridiculous resolutions) from nvdia looks very intresting and is not so expensive and in performance its not so far behind 4870 (which is very good choice too) plus you get some goodies like physiX and CUDA (ok its not really used now but maybe in future?), if you don't intend to do gaming 3850 from Ati is cheap and should do fine. Other than that nothing to change, in RAM departament you are all set, no need for more HDD's or other stuff. If you don't want to do anything yourself I would advise to look for cheap i7 desktops, they can be found for really good price and you get top notch hardware inside like lets say this one: http://www.newegg.com/Product/Product.a ... 6883227123 though I would look farther, maybe you can find somehing cheaper/better. If you won't go for new i7 then just upgrade your PC, buying new 775 desktop is not worth it as you can get all of it cheaper by upgrading. But before you buy anything check what motherboard you exactly have and what processors it supports so you won't spend money for nothing, also your power supply doesn't look very immpresive at 305 W, check power consumption before installing new stuff and buy new power supply if needed (not very expensive, and if you want, you can also buy one with whole case if you feel like it), and don't belive what producers of gfx cards say, you don't really need 500-750W power supply to run single card, check card reviews for real power consumption.