Hi Christy!
I also live in Texas and you do not need to join either one! You can homeschool without it. BUT if you want to support either one and be aware of the laws, be informed, etc. etc., then you could do research on each and join which ever you prefer.
Texas is one of those "blessed" places to homeschool in that you do not have any stringent state requirements. Now... your neighborhood might be another story!
Check out this link, it might help you
http://www.hslda.org/laws/analysis/Texas.pdf
By the way...I hope you enjoy LHFHG - we LOVED using it for Kindergarten!
Dorla