do i need to migrate to multisite?

Hi,
I am taking over the administration of a relatively new site that is a single wordpress install. They would like to have a small store, which I have done using marketpress, and adding the subdirectory /store.

Since this is an already working site (has some posts, lots of pics, etc.) is there any way to add a store without having to activate multisite? I am just worried about transferring all the tables correctly, etc.

Thanks in advance,
ccmb