Building a PC sort of---Compatibility Questions

I have a run-of-the-mill gateway desktop(AMD X2 5000+ 2.6 Ghz, 2 GB RAM, *added* nVidia 8600GT) and I was looking to update it with an Ati HD 4870. I have a pretty weak power supply (~300 watts) so I know I need to upgrade that too. I was doing research on the length of the HD 4870 and found out it definitely won't fit in my case, so I'm also getting a new case.

Case-Rosewill Conquerer-http://www.newegg.com/Product/Product.aspx?Item=N82E16811147104

Graphics Card-Ati HD 4870-http://www.newegg.com/Product/Product.aspx?Item=N82E16814102797

Power Supply-OCZ StealthXStream 600W-http://www.newegg.com/Product/Product.aspx?Item=N82E16817341010

So if you read all that you'd see that I need to transfer most of the internal stuff from my old case to my new one. It's pretty much like building a new computer, which I've never done. So my question is, do computer parts pretty much all work together? Will my motherboard fit with the new case well? Will all the ports and stuff match up?

I've already ordered these parts so...I guess this post is just a result of nervous afterthoughts:). Thanks.

Only problem I see is that on the back side of the case (where the ps/2 ports, usb, lan port, serial port, etc... are). The metal part that comes with the Rosewill case may not match up, and I'm not sure if you can take if off of the gateway case. No big deal really, if the part on the rosewill case doesn't match you can take it off. It'll look a bit funky but its not like you're going to be looking at the back of your case that often.

Here's a pic of the part I'm talking about

I wish you hadn't ordered those - the StealthXStream units aren't all that great, and I've seen quite a few users who have had them fail after a year or so. You could have picked a better case up for that price as well, like the Antec Three Hundred or Cooler Master RC590. And looking at that case, there is a distinct possibility that the HD4870 won't fit. It's 9.5" long, which is a fair bit past the edge of your motherboard. Looking at the construction of that case with the 5.25" bays extending all the way down the the bottom of the case it's entirely possible that the card won't fit. User revies claim that 9" long cards (like the 7900 series, 8800GT, and a few others) are a tight fit, and that extra .5" might make things impossible, especially since you have to hook two PCI-e connectors up to the card hanging off the edge. I also highly doubt that your motherboard has any extra 3-pin headers for the case fans, so you're going to need to get some 3-pin to Molex adapters in order to use the case fans.

I don't forsee any problems actually installing the motherboard into the case, the days of companies like Dell, HP, Sony, and Gateway using proprietary motherboard designs are long gone (since before the days of the X2 5000+ at least), so it should be a standard ATX design. The power supply mount in the case might not be, but since it's getting replaced, that should not pose a problem. The only problem is the one I already pointed out, which is the case itself. The design really is terrible on it the more I look at it, I really do wish you hadn't bought it before asking about it. I'm not saying your card won't fit, but it's going to be pretty damn close.