Expand the C partition in Vista without loss of data

I have a notebook with 2 partitions C (20G) and D (60g).Vista is installed on C.i want to install windows 7 but When i try to installing , it stops, because the in C disk there is little space available.please Someone can tell me how i can expand partition without loss of data.
Thank you.

creating or expanding hard drive includes formatting and and if you format data will lost so no option till you arrange alternate disk for back up your data .there is no possible solution without doing this.

try Acronis Partition Expert is the only disk partitioning software that allows you to automatically or manually resize, copy and move partitions without losing data. Now Acronis Partition Expert is named Acronis Disk Director Suite. It also lets you reorganize the hard disk drive structure, protect your data by creating separate partitions for your system, applications, data, pictures and movies, optimize disk space usage and much more..

If you have some not partitioned space then you can increase the c drive or you have to change d:drive size run the Disk Management check here http://support.microsoft.com/kb/309000
use tool like PARTITION MAGIC that is helpful for you

it is always risky to play with the partitions and agrees to have a copy of security data at least, before groped experiments,
Partition Magic is NOT compatible with Vista,

You want to decreased the D partition, but I imagine that the unallocated space freed is not contiguous to D. Perhaps this is why you can not expand C.

you can delete the D partition with the tool in Vista (of course in this way lose data and programs that you are inside, then a backup is still required), increasing C and D re-create in the space remained.