Your INC comes with "8Gigs" of internal memory. The reason for the quotations is that 6.60Gigs of that 8 are what's available to you, the other 1.4 are used for the OS and other nifty stuff on the phone like preloaded widgets, apps, HTC Sense, etc.
As repeated here, you should be able to have those apps stored on the SD card if need be, but you've more than enough room on the phone as it is. Also remember that your phone only comes with a 2Gig memory card, so it will fill up much faster than your phone (initially), and you can expand the INC sd memory all the way up to 32Gigs. (Also note that has to be SD 2.0)
Stick a larger capacity card in there and your problems will disappear. You can find them cheap nowadays online, I've seen 32Gig cards for as low as $50 bucks, and even cheaper if you really dig. Trust me, it's a worthy investment for your phone.
I also highly encourage you to check out the app that Tigerdango suggested, Astro File Manager, it's a free download in the Market, and will give you great file management capabilities, as well as the ability to create new folders and move things around.
Hope all this has helped you so far.