I know FreeBSD has USB support, since it's one of the choices when you recompile the kernel. I don't know whether the new Linux kernel will support USB better, though.
FreeBSD has nothing to do with Linux directly, although the Linux and FreeBSD often share benefits of open-source development, such as GNU software (gcc, etc...) FreeBSD *is* Unix (deriving directly from the original AT&T/Berkely software), while Linux is a Unix clone, although sharing most of the same advantages.
FreeBSD runs just about any standard Unix software, but also, supports running in a Linux compatibility mode, so it can run any Linux-specific software out there also.
I feel that FreeBSD is definitely better as a server, being probably the stablest OS out there right now, with great network performance. (Actually it is considered common knowledge now that Microsoft has used quite a bit of open source BSD code to improve their networking software -- FreeBSD's license does not prohibit that the way Linux does)
As a desktop, I will say that Linux probably requires a little less work "out-of-the-box" to get a nice desktop up and running, making it a little easier to set up sound cards, etc..., maybe supporting some hardware that FreeBSD can't, but in the end, there's almost nothing Linux can do that FreeBSD can't. (actually, FreeBSD was first to support the fast ATA-100 IDE drives)
If you go with Linux, though, I feel the best "desktop-oriented" Linux out there is Mandrake, while Slackware or Debian Linux are probably a little more server-oriented. I think RedHat has unfortunately sacrificed a bit of stability for a ton of features that they feel business users want, and are in danger of becoming just a little Microsoft-ish.