Options when buying Vista...

I'm currently running XP - it was installed when I bought a pre-made rig from Ibuypower or whatever it's called (yeah, those were the dark days before I learned to build my own). I've pretty much gutted the thing except for HDD and subsequently OS. Now, I'm going to make the upgrade to Vista. Here are a few questions:

1, I'm not certain, but I think my XP disc is toast. I tried loading it onto my Macbook Pro to use with Parallels and continually got an error preventing me to finish the install. I'm pretty sure that it's the disc (I previously had the same version of XP loaded on that laptop, but my HDD fried and I had to reinstall, so please don't come at me with any Mac hate - I'm sure that's not the case).

If the disc is toast, will I still be able to use the upgrade version of Vista? I didn't know if I would need it (the disc) for anything. My serial numbers are still good, I'm sure, and I have those, but I didn't know if, for any reason, I would need to validate or some other business using the original XP disc.

2. If I would need to buy the full version of Vista (not the upgrade), what is the downside to buying the OEM System Builders version from NewEgg? http://www.newegg.com/Product/Product.aspx?Item=N82E16832116488

Since it's so cheap, I'm guessing there has to be a downside. If there is (or isn't), does anyone recommend that?

That's all for now. Thanks in advance for your help! 

(Edits for grammar) 

To install XP on a SATA HDD you need to install the drivers from a floppy disk or have a motherboard where you can use IDE mode instead of AHCI.

The only difference of an OEM version is that you can only have one installation at a time.

There was something about being limited to number of installs with the OEM disc but i think it's a bologna. X360PS3AMD05

Install only once - no transfers allowed Another restriction of the OEM license is that after you install the software on one computer, you can't transfer it to another. If you want a copy of Vista you can install on one computer today and later use on a different computer, you must purchase a full-priced retail copy. If you replace the motherboard in your computer, you also can't continue to use the OEM copy of Windows Vista on it. Microsoft considers a motherboard such a significant component that, when you replace it, you have created a new computer. The OEM copy of the software will then fail the validation, and you should purchase a new license to continue using Vista. windowsaboutcom

I found this after Googling OEM Vista: [quote="windowsaboutcom"] Install only once - no transfers allowed Another restriction of the OEM license is that after you install the software on one computer, you can't transfer it to another. If you want a copy of Vista you can install on one computer today and later use on a different computer, you must purchase a full-priced retail copy. If you replace the motherboard in your computer, you also can't continue to use the OEM copy of Windows Vista on it. Microsoft considers a motherboard such a significant component that, when you replace it, you have created a new computer. The OEM copy of the software will then fail the validation, and you should purchase a new license to continue using Vista. jazztrumpet5

OEM copy's that came with pre-builts are usually tied to the motherboard, or a motherboard from that specific company. Retail purchased OEM copy's are just like retail, just without the box, and without the 90 days of support.

I own 2 copy's of XP OEM and 1 copy of Vista OEM. They can be installed on as many PC as you like, as long as it is only on a single PC at any given time. I have switched motherboards with my OEM OS's multiple times. Worst case scenario is that you use all of your automatic activations and have to call MS to get a new key.

Now I think that MS worded the licensing so that they could restrict OEM to just one PC and one motherboard.  But when I have called to reactivate Windows. all they ask me is how many PC is this copy of Windows installed on.  They have never asked me if I am installing it on a different PC, or if I switched the motherboard, heck, I have told them that I switched motherboards before and they were just fine with it.