There's room for one PCIe GPU, though heftier dual-slot cards will block the only PCI slot, up to four 4GB RAM modules, two 3.5-inch HDDs and one 5.25-inch optical drive. Connectivity includes four SATA II ports, one eSATA port, various USB 2.0 ports, gigabit Ethernet, a 4-in-1 card reader, S/PDIF output, as well as two fan 3 or 4-pin fan connectors.
The SH55J2 ships with a 300W 80-plus certified PSU, which doesn't leave much headroom for anything special on the graphics front, but it should power most low-end GPUs just fine. It also comes with the accessories you might need to get a build off the ground, such as SATA cables, screws, thermal compound, and a Windows driver disc.
Units are currently shipping on Europe with an MSRP of €251 or about $324, which will probably amount to more than $550 after you factor in a CPU, HDD and RAM.