If I have more than 5 and less than 10 returns to e-file can I purchase two CD's/Downloads and install on the same computer to complete the returns?

It won't work that way. You can prepare as many as you want with a single CD, but the IRS efiling limit is 5.  If some of the returns are simple, try TT Free Online or here:

www.taxfreedom.com

TT is not licensed for use by paid tax preparers.

Sorry, no.  The 5 e-file limit is set by the IRS, not turbotax.  Pick a few to file by mail, it will only add 1-2 weeks to the processing time.

I think it might might work if you install the separate CD on a different computer - not certain.