Can you go to a Hindu temple if you aren't Hindu?

Yes you can. Though you won't be beaten for dressing immorally, you may be stared at, if in India, or tried under law for violating conduct. Dress normally, I mean no revealing attire. Jeans and top will do for you. No rigid customs are followed in temples. But it would be better if you cover your head with a cloth before entering any religious place in the Indian Subcontinet (India, Pakistan, Bangladesh, etc.). Even though this head-covering is symbolic of some deep spiritual meaning, some may be rigid on their stance of getting the visitors' heads covered. Moreover, you're considered decent with heads covered and won't look odd among other devotees.

And obviously, no footwear permitted inside the temple premises. :)

Refer to these links for better clarity on covering your heads before entering Temples, Mosques, Gurudwaras, etc:

http://www.musicsongz.com/wp-content/uploads/2011/...

http://www.google.co.in/imgres?um=1&hl=en&safe=off...

http://i.ytimg.com/vi/kz2O2HMr8t0/0.jpg

http://farm1.static.flickr.com/8/8404730_5b1214c52...

http://wearabout.files.wordpress.com/2010/02/dsc_0...

Yes, you can. You can wear salwar suit. Or sari. or even jeans that is not obscene. People would stare but not ban you. Ensure you take bath and do not wear any footwear inside temple.

Buy some flowers and sweets, coconut and other offerings then enter the temple, look what others doing, follow them.

There is no hard custom to put cap, cloth on head, but you can do it.

some yu can go and some temple only allow Hindus

for ex . trimbakeshwar Shankara temple where there is clear sign on doors that Non Hindus are not allowed

Dont wear white, it is color of widowhood

Leave your shoes at the door, at the shoe rack

Drop coins into the Hundi- collection box