I have 2 machines running Linux, although only one is actually used for anything specific.
My HTPC/File Server/Download Box and sofa browsing machine (that actually get's used for quite a lot of general web surfing, almost as much as my desktop which runs W7)
Celeron G530 2.4Ghz Dual Core
Asus P8H61-M motherboard
4GB of RAM
320GB Seagate drive for the OS and programs (this is quite old now, I had this back in the A64 days iirc, but it still works fine)
2 x 2TB Seagate Green storage drives
1 x 1TB Hitachi storage drive.
Xubuntu 12.04 'Precise Pangolin' ...I just love saying the name
This machine uses the integrated graphics and the cpu being a Sandy core Celeron is actually surprisingly fast, it's genuinely quite a powerful little cpu, considering it cost me less than 30 quid a few weeks ago, I replaced an older AMD dual core system with it. For so little money though, it does make me stop and think at just how capable it is and how hugely overpowered and expensive my desktop is by comparison (that's a 3570K at 4.2GHz now). If I put a decent graphics card (and an SSD) in this machine, it could probably do everything I would want to be perfectly honest.
My other Linux machine is just something I knocked up out of old bits I had in the loft for no better reason than I felt like it. I don't use it for anything in particular, then again I don't really trust the old Antec psu it's using.
Athlon 64 3200+ (venice core iirc)
MSI motherboard of some sort, has socket 939 with AGP so iirc that would be nForce 3 as nForce 4 was PCI-e.
1GB of rather fancy looking OCZ ram.
320GB Seagate drive (the sister drive to the one used in the above machine actually)
Geforce 6800GT graphics card, also my last ever AGP card.
Good old Lian Li PC7 case.
This is actually running Mint Debian Edition 201204 right now, with mate, which I really, really like. And I would love to use on the HTPC/Server but ...I can't get the Cougar Point HDMI sound to work with it for some reason, everything looks like it should, every indicator says it 'should' be working, but it isn't. So unless I do manage to get it going, LMDE will stay a toy on this machine...which is a shame as it's so clean and fast, more so than any Ubuntu derivative I have used ...and I've used pretty much all of them.
I was thinking about having a play with Centos on this machine, I might do that when I get a chance.
I love that backdrop, where did you get it from ...and do you have a link by chance?