Hi George,
You should have your toes pointed slightly outward and the distance between the feet about the same width as your shoulders or just slightly wider.
When learning to get up, stay down crouched as long as you can and don't stand up until your board is planing on the water.
If you poke around here on Wakeworld, there is a good article or two on how to get up. For example this one:
http://www.wakeworld.com/Articles/2002/GettingUp.asp There are also some great training DVDs like "Higher Education", "Detention" and "Waketrix". These all take you from beginner through intermediate to advanced.
BTW, no tower is necessary to have fun in this great sport. If you get hooked like the rest of us, you'll no doubt want one later but for now, use what you have and enjoy. You can always add an after market tower to your boat if you like, or opt for a wakeboard specific boat. Since you already have a boat, enjoy it, and practice getting up and riding. You'll love it!
Welcome to the sport!