I installed WAMP5 1.7.0
When I try to access localhost & phpmyadmin, it asks for a username and password.
I'm pretty sure that i didn't configured any.
I installed the same thing in another computer, and it worked.
what could be the problem?

IIRC the older versions of wamp had a default root user (named: root) without a password.

Any specific reason you've installed 1.7, and not 2.0 ?

I've been using wamp 1.7 , not any other particular reason.
I tried 'root' and empty pasword. it didn't worked.

If I instal wamp2 and export my databases there(which i created in wamp 1.7)..will thr b any problem.??

plz me some instructions on how to setup wamp2 with an account with a password(i mean a user)

You can create a password in phpmyadmin, in the priviliges section. There are some settings that you can change in the config file of phpmyadmin, whether or not it should ask for your password, or just use a specific user. (http://www.phpmyadmin.net/documentation/Documentation.html#config see authentication mode).

Don't know about the mysql version in 1.7, but in 2.0 it uses 5. Unless you use some very specific features, your sql will import just fine.