Purchase of existing retail web site

Hi, our company just purchased a retail web site that has been in business for 4-5 years. It has no sitemap, robots.txt, or anything related to SEO. Google has indexed the site and has found over 200 Url's. Most of them are query-string based (ex: product.php?ProdID=462&Prodvar=4). The titles and meta tags are also the same for every page.

We are going to be re-writing the site soon, but until then:

1. Is there any advantage to adding a sitemap right now?
2. Is there anything else I can or should do to the site in it's current state to improve (or maintain) seo?

Thanks!

You say that you are re-doing the site, so finish doing it first...
seo is a marathon and not a 100m sprint (I read somewhere in this forum, garythescubaguy?)
Titles and meta tags being the same for every page etc. is all bad, good thing you are re doing...

I would also analyze the backlinks the site is getting if any and see what URLs or pages on your site they are pointint to.
Would be useful in planning your linking strategy when the new site is up

If you're doing a rehaul I would suggest hiring an SEO professional to do a lookover before you launch full. It will save you a lot of hurt and questions over the long term. Delaying your promo until you've actually swept the floors and stocked the shelves makes sense.