what do you mean a PRO?
simple, after 4 years 14 hour/day practicing and and "
high" national rank usta/lta e.t.c contact the ITF via the website for a ipin. After that if you are lucky enough to be accepted sign in to qualify for a "easy"(by pro standards) 128 qualification draw futures tournament(the lowest ATP ranking point competition series) e.g India/Kuwait/Columbia/Spain and if you get into the main draw via qualification(4 games/2 days) or W/C if you are rich and win get to the last 16(up to 6 games over 6 days!!) to get 1 ranking point and $216 prize money. Congratulations you are now a tennis pro!on top of the $1000+ you spent on travel costs/physio/equipment/food/accommodation
seven years ago Nikolay davydenko was living in his friends car whilst traveling around Europe playing challenger series tournaments trying to make ends meet!!being a "pro" isn't as glamorous as it sounds unless your mommy and daddy are loaded during the early years .
If you want to be top 100 then forget it, i am sorry for being negative but tennis is one of the hardest sports to make a
decent living from. you need over 15,000 hours (thats 3 years 24/7 365 if you are a cyborg) training/serve over 2 million balls to make it to the top 300.
the 500th ranked ATP "WORLDWIDE" tennis player earned $9000 in 2006. According to the
atp website so far this year the 500th ranked player has only won $408! Imagine how much the 500th ranked football (soccer) player "WORLDWIDE" earns a year ($4,000,000+ according to wikipedia).
If you want the fame and fortune i suggest another carrier path.