Install Windows 2003 Server R2 Std on PowerEdge 2950 without Floppy

Try this:

http://support.dell.com/support/downloads/download.aspx?c=us&cs=08&l=en&s=bsdr&releaseid=R237984&SystemID=PWE_2950&servicetag=&os=WNET&osl=en&deviceid=13724&devlib=0&typecnt=0&vercnt=3&catid=7&impid=-1&formatcnt=0&libid=7&typeid=-1&dateid=-1&formatid=-1&fileid=342467

Or this:

http://support.dell.com/support/downloads/download.aspx?c=us&cs=08&l=en&s=bsdr&releaseid=R251661&SystemID=PWE_2950&servicetag=&os=WNET&osl=en&deviceid=24134&devlib=0&typecnt=0&vercnt=1&catid=36&impid=-1&formatcnt=0&libid=36&typeid=-1&dateid=-1&formatid=-1&fileid=367903

You can use nlite to slipstream the RAID drivers into a 2003 disc; should be plenty of docs/support at the nlite site (see below).

Surprised that the USB thumbdrive didn't work -- you sure you enabled/changed the boot order in the BIOS? You can also buy USB-to-Floppy drives -- believe they're meant as a laptop accessory but I know I've used one before for driver disks.