You can't really compare the PS3 to a PC spec-for-spec, but if you were to...
The PS3 has the Cell (1 PPE + 8 SPEs (1 disabled, 1 dedicated to Hypervisor), all @ 3.2GHz). While it's not much of a multi-purpose processor (for desktop usage), it's amazing for certain tasks. If you want something to "match" the PS3's Cell, you need a CPU that's great at parallel processing, but mediocre at other things. An entry-level Core i7 should blow the Cell away on the desktop.
The PS3 also has 256MB XDR RAM (Rambus). This is clocked at 3200MHz. What's better than this? 4GB of DDR3
The PS3 has the RSX, an admittedly shameful GPU based on an old nVidia. Most modern graphics cards should annihilate it.
The big one is the PS3's Bluray drive. It may not be able to write DVDs and CDs, but it IS able to read Bluray discs. One of those for your PC would set you back a fair amount. Think R1000 - R1500.
By now you get my drift: you can't compare the two in terms of specs.
If you want a simple no-nonsense gaming platform, get a PS3. If you want a versatile gaming machine that can play games at the same level as on a PS3, buy yourself a mid-range gaming machine (Core 2 Quad, 4GB RAM, 4890), and a PS3 Dualshock3 controller
