I'm not 100% on this as I did the individual installs, however, I think that when you do a WAMP install rather than doing individual installs for Apache, MySQL and PHP it assigns the default mysqladmin password as "root" rather than leaving it blank.
Try doing the following;
Run command prompt from the windows start menu (search cmd or go to run and type in "cmd") and type in mysqladmin -u root -p status and when prompted for a password type in root. If MySQL is installed and running correctly it should return something along the lines of;
Uptime: 102261 Threads: 1 Questions: 1 Slow queries: 0 Opens: 15
Flush tables: 1 Open tables: 0 Queries per second avg: 0.0
After checking that, you can then change the default password by typing mysqladmin -u root -p password "newpassword", where "new password" is your desired password. You will be prompted to put in the current password, which as I said, I believe is root.
You can then try the first command again this time using you new password to ensure it has changed. Again, it should return something like the quote above.
I'm pretty new to this so I may be wrong but give it a shot, let us know what happens.
Hope this helps.