Cannot create new primary partition on Windows Vista

I am not able to create a new partition on Vista through Disk Management. I want to install Ubuntu and for that I need a separate primary partition. But there is no way to find the same. When I try to create a new partition I am getting a error -- You cannot create a new volume in this unallocated space because the disk already contains the maximum number of partitions. I cannot install Ubuntu if there is no primary partition on my system. The C drive has Vista and there are two more which has data. I had shrinked one and extracted 20GB out of it. But I cannot convert that to primary partition.

It is a bit complicated I think. I am also trying to do the same. But in my case I created the partition at the time of Vista installation. A OS needs primary partition to boot. It cannot work on logical. You can try Vista bootable DVD for that. Boot your system with Vista Installation disc and then click on Customize. In that delete the 20GB partition you had created and then click back on it and choose Create. It will ask you to add this as a primary or logical partition. If you get that option then you would be able to install Ubuntu. And also you have to provide a 10GB swap space for better performance. 10GB is quiet higher you can allot 5GB also. This swap space is the virtual memory of Ubuntu. If your physical ram is used completely then the OS uses Swap space to perform a number of different operations.

If you are not able to create a primary partition then the issue lies with old mbr. There is a system reserved partition which has all the information about system partitions. If you remove that all partition will disappear. It is a bit risky. There is one more easiest option you can go for. You can install Ubuntu inside Windows. It will appear in Control Panel and from there you can remove it whenever you want. I am using the same in my laptop. Both Ubuntu and Windows share's one and the same partition.