Advice regarding Google XML sitemap plugin

Hi

I have successfully used Google XML sitemap 3.0.3.1 on my other blogs on WP 2.3.3.

My new site is now WP2.5, which im very happy with the improvements, and intend to install Google XML sitemap on this site.

Could anyone please advise me on the best route to take for my dilemma?

I have the WP install at my route,(www.mysite.com) I also have a ecommerce solution in (www.mysite.com/store). I want my urls for the store to be in my sitemap also.

1) What is the best way to acheive this?

2) If I add my store urls to the generated sitemap.xml that is generated in WP would these urls be overwritten when I add a new post or page in WP?

3) Would Google pick up 2 sitemaps? I.e the sitemap generated by WP in my route and another sitemap in myroute/store. Am allowed to submit 2 sitemaps and if so how?

Any advice on how to acheive a solution would be most welcome, and thanks in advance for any assistance offered.

Regards
Voddie