There has never been anything Wrong with Vista. (of course there have been bugs, like any OS)
The big issues have been manufactures supporting older devices. If you had something manufactured before Vista it was hit and miss if the mfg made a Vista compatible driver. It's harder to program for Vista. Since there is a huge XP customer base, manufactures have been slow to put resources into programming for Vista. (always about the $)

What makes it harder to program for is what also make it's more secure than previous Windows OS's.

No, you would have to buy XP.
If your system came with Vista, it will run fine and may be hard to find XP drivers for it.

Yes my XP out of the box runs faster than my Vista out of the box. If you want the fastest system, just install Windows 95.
My point being as new 'features' are addeed it has been historicly slower than the previous system. Windows 98 ran faster than XP on a CPU with less power and resources.
If you want to speed up Vista you can turn off some of the features that are enabled by default. Search indexing, sidebar and Aero Galss (the pretty stuff) are a few that can all be turned off and will give you a noticeable speed increase.

Why run Vista over XP. The One big reason would be it's more secure. With things built in, like Windows Defender, UAC (user account control), Windows Firewall, parental controls etc. Security and safety features new to Windows Vista - Wikipedia, the free encyclopedia

If you do any multimedia, it also has built in features like tags for photos, easier access to media from my networked devices, etc.
Vista's Multimedia Features and Accessories - PC World

And of course Windows 7 will be out in about a year.
http://windows7news.com/tag/windows-7-release-date/

As far as the crashing, with many windows open. It could be many things, generally make sure your OS is up to date and you have the latest driver updates for you video card. Also making sure your browser (IE, Firefox, or Opera etc.) and Java is current.