Mercury
I am currently employed in a decent clinical/basic sciences lab where the guy who trained me (and whose project I took over) was actually a Medical Doctor (I believe they call the degree MBBS as in the traditional British system) from Pakistan.
He has just begun (~2 months ago) his neurosurgery residency at UPENN. Wow. He did very well on all his boards, and more importantly, had great recommendations...
Anyway, in answer to your questions, I think it is more than very possible for international medical graduates to get advanced research positions. In a lot of cases, I think that many (from discussing with him) IMG's have to do so in order to maybe overcome any stigmas residency programs associate with this. In his case, I know he was first maybe hired as a consultant physician, and then when he transferred to the labs at the hospital, he became a faculty scientist (I'm assuming same/close pay to postdocs/PhD's that aren't PI).
I would first make sure you find a good research hospital with labs currently seeking projects you are interested in, and search postings on their human resources page. If not, you can always search individual's labs and try to contact them. I could be wrong here, but as my PI is MD/PhD, other MD/Phd faculty could be more receptive to the plight of a medical student...but who knows.
As far as research wise, I think several factors come into play when applying to residencies. If you can do advanced clinical research, of course that is a bonus. But basic sciences research, especially that with a high clinical significance/application, would absolutely not hurt your CV at all...especially if you get published in a better journal, faster, as well as gain recommendations. I know in my former colleague's case, he also was very active at the ALS/Muscular Dystrophy clinic (since the big boss was the head physician/head of neurosciences and attended patients there)....
Hope this helps.
ebizzle
I was wondering if it would be possible to get your colleague's contact (the one at UPenn). I would just like to email him and ask exactly what he did to get the position you mentioned. Feel free to PM if you would not like to share this info on the forum.