How to verify ancient DNA is not modern DNA? - (Apr/11/2006 )

Does somebody know how to verify the results obtained from analysis of ancient DNA?
As far as I know, when I have the DNA sequence extracted from ancient speciment, to make sure that it is not contaminated with "modern" DNA I would blast this sequence to find out if it shows similarity with sequences from related organism. What other ways can I use to do that?
My another question concerns the major problem of "ancient DNA" studies, why this research has a great burden of proof than "modern DNA" studies?
Is this just because the ancient DNA could be easily contaminated with other DNA or because it is very degradated and it is hard to use it for molecular studies?
I would be very grateful for any suggestions or links...

There was a mommoth DNA sequencing paper in Nature about a month ago. I would check that article if i were you.

Try this:
Extensive human DNA contamination in extracts from ancient dog bones and teeth.
Malmstrom, H; Stora, J; Dalen, L; Holmlund, G; Gotherstrom, A
Molecular Biology and Evolution (2005) 22(10): 2040-2047

Thanks a lot ! :-)