Can you make a ATV street legal in Texas?

That will depend on the state but at the very least you will probably have to equip it with head and tail lights, break lights, license plate light, turn signals, seat belts, etc.

Here is what is needed by law to operate an ATV on Arizona roads:

Headlight (hi/low beams)

Tail light with brake light

Rear view mirror

Horn

Registration

License Plate (Must say MC not RV)

Insurance

Motorcycle endorsement on your driver's license