Folder size in Win 7 - how to know whats taking up all the space on my hard drive ?

Windirstat will represent folder and file space in a graphical format, helping you determine what is taking up your space. Also can be sort by file type.

Link is provided below.

http://windirstat.info/

I'm a huge fan of NirSoft's (free!) utilities:
http://www.nirsoft.net/

One of them is FoldersReport:
http://www.nirsoft.net/utils/folrep.html

Here's a description from the NirSoft website:

"The FoldersReport utility scans a drive or a base folder that you select, and displays essential information for each folder that it finds: The size of all files inside the folder, The real files size on the disk, number of files inside the folder, number of hidden files, number of compressed files, and number of subfolders. You can use this utility to easily find out which folders use the most space in your drive. You can scan the folders of your local drives, CD-ROM drives, and network resources on a remote computer."

Although the System Requirements section doesn't mention 32-bit and 64-bit W7, I've run it in both without a problem. Here's a screenshot from an execution on a 64-bit W7 system:
Regards, Joe

you dont happen to have a Lenovo, with R&R ?  then uninstall it and remove the backups
(take on on an external drive)

that makes backups on the same disk, and consumes your space fast  http://support.lenovo.com/en_US/product-and-parts/detail.page?LegacyDocID=MIGR-4Q2QAK

Have you received the info you were looking for? Ready to close and award points?

Thanks everyone.

I went for Tree Size Free