It is /almost/ essential to have a PhD in CompSci/EE from a top school to do HFT. Alternatively one should demonstrate extensive hardware/networking and optimisation skills obtained from other low-latency industries.

All of the top work is being done on FPGAs and latency is now on the order of microseconds (probably lower).

As for lower frequency algorithmic trading, that is a game that one can play at the 'retail' level if you're willing to spend (quite a lot of) time learning.

I run a website about algo trading. If you want to get a taste for what is involved have a look at some of the articles here: http://quantstart.com/articles/#algorithmic-trading