Well the straight answer is, yes. How do I know?
Well my school only allows 5 IGCSE's, probably due to the fact that it mirrors what domestic students do in New Zealand (although having said that my school is not an international one nor am I an international student). Regardless, the point is we only do 5 subjects in 5th form so we only take 5 IGCSE's. I know that all schools that offer CIE in New Zealand, including AGS (my school
) have a system where you take 6 or 7 subjects in the 4th form, drop a few (usually compulsory subjects like latin) and only study for 5 subjects in IGCSE.
So this is a pretty normal thing. Regarding university entrance (I will assume UK) last year 2 students from my school went to Cambridge (1 for economics and the other for English). Plus I think my friend's brother is going to Manchester in 2010. So the straight answer is yes, it is possible. However, at AGS, we also do 5 subjects at a-level (for A2 we do 4). Although not compulsory, most students take 4 A2's in their final year at school (although the guy who's doing eco at Cam did 3A2 and 1 new AS).
Thus, I think the point is, yes IGCSE is important but it seems a-levels take precedence, which they should in my opinion as IGCSE's are too easy.
Hope that helps! (sorry for the long, rather personal post)
*If anyone wanted to know, the two Cambridge guys were straight A students as well as being senior prefects (I think the eco guy was deputy head prefect - he was a bit of a legend)