Generally C++ is the dominant language (although Java is growing), unix the platform (Solaris and Linux mainly). I know at least a couple of firms that are embedding code onto programmable network cards for equities trading.
If you go to the eFinancialCareers website and search for "low latency" you can see the kind of thing recruiters look for.
In terms of problem solving it's not that different from other areas. Concurrency is obviously very big (lock free algorithms, etc) as is being comfortable with low-level stuff. You don't need it all the time but sometimes you do need to be able to read through kernel code and get an intimate understanding of things like tcp/ip.
If you go to the eFinancialCareers website and search for "low latency" you can see the kind of thing recruiters look for.
In terms of problem solving it's not that different from other areas. Concurrency is obviously very big (lock free algorithms, etc) as is being comfortable with low-level stuff. You don't need it all the time but sometimes you do need to be able to read through kernel code and get an intimate understanding of things like tcp/ip.