1. I don't know whether it's the hottest or not, but I do know it's not easy to find a job in Bioinformatics, especially with only a B.S.
2. If you are interested in it just because you think it's hot, then don't study for it. There are plenty of other areas in either CS or Bio, say, computer graphics and cancer biology, that are as hot as bioinformatics while kind of easier (in the sense that you only need one major...)
3. But if you do like working in the interface of life science and the digital world, there are several ways by which you can get yourself involved. None of them is that tough as you think.
1) If you are in SOC, take some life science courses -- genetics, molecular biology, biochem, organic chem, biostats, etc. And do researches with those professors who are active in this field. To name a few, Prof. Ken Sung, Prof. Roland Yap, Prof. Leong Hong Wai, Prof. Tan Kian Lee, Prof. Leong Tze Yun (Medical informatics), and Prof. Anthony Tung. Their researches range from database, AI, to algo -- the three pillars of Bioinformatics.
2) If you are in life sciences, take some CS courses, or maybe IT minor? I'm not sure 'cos I don't know what they are teaching in this minor... But at least you should learn programming, especially in perl, database, machine learning, etc.
3) If you are in engineering, simply take the Bioengineering track, and look out for research projects in Bioinformatics.
Make sure you start early, either in your first year or second year. Although CS ppl can take Bioinformatics-related HYPs in their final year without any bio background, I personally don't think that can be called "involved" in this field. Without certain amount of biology knowledge, they can't go too far. Especially, nowadays the majority of what is interesting in Bioinformatics is no longer just algo+comparative genomics, but complex system biology. And turning to either the job market or graduate schools, education in both bio and CS fields is a requirement.
And for bio ppl, without any CS background, I'm afraid they can't do bioinformatics at all...
4. There are lots of graduate training programs in Bioinformatics, in SOC, life science department, engineering, the Bioinformatics Institute (which provides a program leading to a degree in Bioinformatics), and NUS Bioinformatics Center.
