Unidentified Case Parts

Hello

I am a first time builder and am currently building a new AMD setup. I just got a CoolerMaster Centurion 5 ATX mid tower in the mail and was setting it up when I came across a couple peices that I could not figure out what they were for. The instructions are extremely bland but here is a picture of the two pieces:

i8.photobucket.com/albums/a8/Snack_Packs/CaseParts.jpg
The plastic part on the right has mounting tape on the back of it. The piece on the left is a little metal "tire" type thing.

Also, when I installed the motherboard to get and idea of how it fit in the case and all, it seems like it is about a milimeter too low, and doesn't Quite match up with the I/O. I didn't forget the standoffs or anything so I do not know why its just a tad too short. It's not too short so that nothing can be plugged in, but it's just a little off. Any ideas why?

Anyway, I haven't finished getting all the parts for my new system yet due to financial status, but so far I have bought an ASUS CrossHair nforce 590 sli socket am2 motherboard, and Rosewill 600W power supply, CoolerMaster Centurion 5 ATX mid tower case, and (2x1GB)Kingston HyperX DDR2800 PC6400 memory. I will probably be getting a Windsor AMD Athlon 64 X2 6000+ processor, a GeForce 8 series video card (don't know which one yet), a couple optical drives, a Western Digital Caviar 320 GB SATA 3gb/s HDD. And then the OS, which will probably be XP because of all the incompatabilities i've heard about with Vista.

Thanks ahead for help on the Case Parts question!

AT the case part beats me no idea...

At the parts for the CPU if you have chosen the AMD door go for that X2 6000+ or a Opteron like this

The video card should be a Geforce 8800GTS 640DDR or at least a 320DDR....

The HDD i would choose a 320GB DDR Seagate with 16 MB buffer

The OS is a though choose...Vista is the future, it is true that it has some issues with some computer parts but that bad....On the other hand XP is more used, it lacks some of the driver issue, also Nilpo with a new computer hasn't got any bugs so ...remains a though choose...