Hiya,
I have grown tomatoes and squash together in the same bed but mine was not a success story. As a general guide, squash are thugs compared to tomatoes and will take over the area they are growing in. So unless you've got quite a big bed, I'd advise not doing it. However, if you do give each squash plant as much room as possible and plant the tomatoes quite some distant away.

I have even tried controlling the amount of room a squash plant takes up by tying the 'vines' onto stakes to encourage it to grow up, but still it swamped the tomatoes. I hope this helps although I'm sure it's not really the answer you were hoping for. Good luck, whatever you decide to do!

Happy Gardening!
Shelley

squash need loads of water whereas tomatoes like to be on the verge of dryness. Have you tried the 'three sisters' method - a north american indian way of growing beans, squash and sweetcorn in the same bed: the beans grow up the corn while the squash acts as a natural mulch and rambles between the corn and beans. In truth, the beans and sweetcorn supporting each other seems to work better with beans planted around the perimeter of the sweetcorn, rather than growing up the corn - probably cos american corn is taller and sturdier than when grown in the UK (but just guessing here). Have also made the same mistake growing cukes and tomatoes together - not a success!