RCA analog is not digial...hence the analog. Also, RCA is only 2 channels (in general, at least. You can have 5.1 over RCA...it just takes a lot of cables.)
SPDIF is a type of format/interface for digital audio. It does not specify what kind of cable to use. Traditionally, SPDIF is done over a "coax" cable, which simply means that two wires carry the same axis, hence co-axial or coax. Really, though SPDIF signals can be sent over any type of cable that has two leads, but the coax cables are better, as the main lead is shielded be the second. Additionally, SPDIF can be sent over optical cables, which use light to transmit data instead of electricity. Your notebook will probably sport a non-optical SPDIF interface if indeed it does support SPDIF at all. Check your manual to find out.
If it can do SPDIF, you'll need a 3.5mm mono male to RCA male cable. If it can't do SPDIF, you're stuck with 2 channel analog audio with a cable that's 3.5mm stereo male on one side, and dual RCA on the other.
More:
on SPDIF-
http://en.wikipedia.org/wiki/Spdif
cable to use with analog audio -
http://www.installer.com/photos/ipod-rca.jpg
cable to use with SPDIF (not optical) -
http://yfrog.com/4yspdifrca35mmrn7j
I should note that the analog audio cable (dual RCA to stereo headphone) can be used as an SPDIF cable if you select the right RCA header to use in the connection (one will remain unused).