Changing URL address for specific pages

[cdx]

Hey all...

I am trying to promote a high PR website with very competitive keywords. (PR =6,7 in most of the pages).

Now, the website ranked very good for few keywords - high competitive ones (web design, building websites... I am not talking about English).

Most of the keywords are leading to links like that :
Index.asp?CatID=391&ArticleID=537

Now, I want to change those addresses to better optimize ones.

Can it cause a drop in the ranking ? Or G will notice this is just a change in the URL ?

Wondering what to do...

Thanks in advance,
Guy

[lizza]

One I changed the URL of one my blog.After that google de-indexed all my posts and re-indexed again.I found no effect after re-indexation.