SNP database for mouse strain - (Jan/08/2009 )

I've been awarded a new project, but completely out of my previous experience.

We need to do a clonality study on our mouse strain C57BL/6 using a X-chromosome inactivation pattern. So we search for an informative SNPs within this strain on X chromosome.

I never worked with mice and I'm bit unaware of all possible tools there are. Is there a database that would contain intra-strain SNPs and not only differences between strains (I found some of those)? So far I'm googling and I found some stuff, but if you could recoment some mouse SNP databases you use and are good I'd be really gratefull.

So, after some search I started using NCBI dbSNP, seems to have all information I can get, but I have some questions about it, if you work with it and can help me, please visit the topic in Bioinformatics. Thanks.