Partition

Hello,
i have 160GB HDD which is distributed in three partition that is
C drive(boot,page file,crash dump,logical drive),
D drive(logical drive) and
E drive(primary partition,system,active)
earlier i have my operating system in primary partition but it could'nt extand it but os needed more space in this partition. then i extend a logical drive and reinstal my os in extended partition.
now every thing is ok.
.....can i face any problem in future?becoz my os is not in primary partition,system.active.
.....can i change my c drive as primary partition,system,active? which is now logical.
if yes wt to do?
plz help me.