It depends on exactly what information you want, but you probably want to P/Invoke SystemParametersInfo with parameters like SPI_GETOEMINFO, SPI_GETPLATFORMMANUFACTURER, SPI_GETPLATFORMNAME, SPI_GETPLATFORMTYPE and SPI_GETPLATFORMVERSION.
MSDN has an example here.
EDIT
Here are some values for you:
#define SPI_GETPLATFORMTYPE 257
#define SPI_GETOEMINFO 258
#define SPI_GETPROJECTNAME 259
#define SPI_GETPLATFORMNAME 260
#define SPI_GETBOOTMENAME 261
#define SPI_GETPLATFORMMANUFACTURER 262
#define SPI_GETUUID 263
#define SPI_GETGUIDPATTERN 264
For the version I'd just pull Environment.OSVersion.Version and compare to this version list.