There will be DNA in all of the above materials, but at low concentration. Nearly all of the cells in the blood (in terms of total numbers) are DNA-free: both RBC's and platlets (the most numerous cells) are anucleate.

Your best bet, if its an option, is to start with whole blood. Spin it down to get the buffy coat (basically, concentrated WBCs) and use that as your source of DNA. The WBC's are the major source of DNA in blood - plamsa, RBCs, serum, etc, will only contain trace amounts.

Another option, if you're really stuck, is to use glassmilk to purify free DNA from the serum/plamsa. Spin down any particulates out of the plasma, mix 10ul glassmilk/ml plasma/serum and incubate at RT (rotating to keep the GM mixed) for 10-15min. Spin down the GM, wash as per the kits protocol, and then elute your DNA.

The only real problem with the above method is that the DNA which if found free in the serum/plasma tends to be highly fragmented.

Bryan