Fileshack posted a demo for the PC version of Devil May Cry 4 today, which you can download through the alternate source. The download weighs in at 804.05 MB. Registration is required over at Fileshack (sad), but I'm sure it's worth the trouble if you're a DMC fan with a honkin' PC.

There's a benchmark tool which you can use to see if your system can run the game, but it's 483.62 MB in itself! So, here are the unofficial requirements:

Minimum System Requirements
OS: Windows XP/Vista
Processor: Pentium 4 @ 3 GHz
Memory: 512 MB (1 GB for Vista)
Hard Drive: 8 GB Free
Video Memory: 256 MB (nVidia GeForce 6600 SM3 Required)
Sound Card: DirectX Compatible
DirectX: 9.0c
Keyboard & Mouse
DVD Rom Drive

Recommended System Requirements
OS: Windows XP/Vista
Processor: Intel Core 2 DUO
Memory: 1 GB (2 GB for Vista)
Hard Drive: 8 GB Free
Video Memory: 512 MB (nVidia GeForce 8600)
Sound Card: DirectX Compatible
Keyboard & Mouse
DVD Rom Drive