I tried looking for a trial download, but was unsuccessful.
I did find this on their site:
Have the minimum computer specifications changed for Version 10?
No: the minimum requirements are still 1 gHz, and for RAM, 512 MB on Windows 2000 and XP and 1 GB on Windows Vista. L2 cache size makes a bigger difference in version 10; we recommend 1 MB for the L2 cache.
IMPORTANT NOTE: Unlike previous versions of Dragon, version 10 requires the SSE2 instruction set for Pentium and AMD processors.
Determine if a computer supports SSE2: There are various utilities available to determine if a computer's processor supports SSE2. The following CPU-Z utility is available for free and is updated regularly: http://cpuid.com/cpuz.php
When running the CPU-Z utility, you should see SSE2 listed in the "Instructions" on the "CPU" tab; if it is not listed, then unfortunately the processor does not support SSE2.
Truthfully, I'd email them and see if Windows 7 is supported.
I looked at Microsoft's site and the C++ runtime states:
Supported Operating Systems: Windows Server 2003 Service Pack 2; Windows Vista; Windows XP