Does it have to be 2k3? Software RAID under Linux and Solaris are rather good.
300Mb(it) is around 37.5MB/s so you loose a fair bit on read speeds too but should cope (just about) with high bitrate HD content streaming. With 60Mb(it) being around 7.5MB/s, writes are painfully slow compared to a decent RAID controller where write speeds can be amazing.
Get a dedicated raid card. Go secondhand and get a enterprize quality card...