when will windows based games be able to be used in Ubunto?

http://www.winehq.org/

Your results may vary

U can't all the games ,but some . If u have good h/w virtualize xp in ubuntu and play .

Windows based games are not "fully" supported under linux.

As others have said you can try and run windows based apps with wine. but id recomend checking the winehq application database to see if the (application i.e game) is listed and what the current status is.

Keep in mind just because a game is listed as working does not mean it will preform as smoothly as it did under windows.

(except for WOW I got a significant FPS increase when I ran it under linux when i used to play)

as another stated above you can run it in virtual box or similar Virtual pc software. However keep in mind again you "May" take a performance hit if your hardware isn't strong enough.

I personally just keep an old dusty win system around strictly for gaming these days, or a dual boot setup is good too...if you don't mind having to reboot.

When will I be able to play my Linux games on Windows?

Wine is a bit of a chore for a newbie to set up, I personally recommend Crossover Games, it may cost £20 but they do a lot of development for Linux and it puts a lot back into the community

I can run some Windows games using wine. I can play Hoyle Card Games, Doom, Quake and other games that I can't think of right now but have had no luck playing games made by Microsoft. I like Age of Mythology but have not been able to make it work. Linux has a lot of good games and Linux compatible games are getting better all the time so the need for Windows Games is getting less all the time.

I agree with Eric952x, try and support the companies that are making the effort to release games for Linux. Here are some that I have ordered from previously:

http://www.rune-soft.com/shop_e/linux_shop/linux_shop.html
http://www.linuxgamepublishing.com/
http://www.tuxgames.com/

I've been playing a ton of Altitude lately. It's ported to Windows, Linux, and even Mac. It actually runs better on my Linux boxes though.