You can download an add-in for Excel called Genalex. It will calculate all kinds of diversity stats, and PCoA, and all kinds of things. Highly recommend it.
Yes! you can calculate heterozygosity of SSRs in excel but what kind of data you have. DO you want to estimate the diversity based on polymorphic markers or have bi-parental population in respect of parents? Please clear little bit about it and I can share R codes that can estimate the whole genetic diversity estimation in a few mins....