You can easily get to Diskmgmt by Start -> Run -> DISKMGMT.MSC
Also, maximize the window to be able to see everything. Then, spread the columns in the upper part of the display, so that you see all the text and numerical values in each column. The default column widths do not show everything and posting screenshots with non-visible data is not as helpful as having everything that's there appear in the posted screenshot.
Anyway, it looks like the two partitions on your first hard drive are properly lettered, C and D.
The second drive's large 287GB primary partition is your current problem, and you want to give it a drive letter. Since you already have two CD/DVD drives and they are E and F, do you want to give this 287GB drive a letter of G? That's one way to go, of course.
Or, you can reassign drive letters for your two CD/DVD drives (making them F and G, for example) and then assigning E to the 287GB partition on the second hard drive.
Up to you. Any of this is possible, and under your complete control.
To change/assign a drive letter to a given CD/DVD drive, or to a hard drive partition, click on it. In the case of the hard drive partition, click on that partition (making it cross-hatched, thus selected). Then right-click on it to get the popup menu, and select "change drive letter and paths...".
You'll then get a new window allowing you to push the "change" button to change or assign an available drive letter. If you don't like the presented default letter, just click on the down-arrow and pick another letter from what's available.
If you push the CHANGE button, you can then do what you want... to assign the suggested letter or pick another one.
Again, if you want to make this 287GB partition E, then you'll first have to reassign your two CD/DVD drives E and F... or at least just the one which is currently E, giving it another letter (say G) and then giving the new 287GB hard drive partition E.
It's all up to you. Left-click on the 287GB partition, right-click and select "change drive letter and paths..." and follow the wizard.