since 1 hard drive is limited to 4 primary partitions, how about using 1 primary and 10 extended partitions instead?

"You can use more than 4 primary partitions, if you hide the extra partitions.

For this game of hiding and unhiding partitions, you need a boot manager.
Some Linux distributions replace the Windows boot manager with another that doesn't suffer from that limitation, although this should be undertaken with great precaution.

The other way to go is to use a product that takes care of the whole thing. Some such products are :

BootIt NG ($34.95)
Support of over 200 primary partitions (if desired). I've used it and it's one of the best.

GAG (initials, in spanish, of Graphical Boot Manager) (open-source)
Allows boot of up to 9 different operating systems installed in primary and extended partitions. Never used it.

Partition Commander 11 ($49.95)
No info on maximum partitions number. I've used it a long time ago and it worked then pretty well.

Norton PartitionMagic 8.0 ($69.95)
Otherwise called BootMagic, no info on maximum partitions number, and seems to only support partitions up to 300GB. Never used it, and I usually stay away from Norton products.

Warning: Before playing with partitions, take great care with your backups."

"I am not sure that you can install Windows 7 on extended partition, however, you can always make virtual disk file (*.vhd) on one of your current partitions, install Windows 7 into it, and boot from there.

Only prerequisite is to have NTFS partition with enough free space."