Hi there, welcome to LQ!
Please do not mark your threads/posts as "Urgent" as this is only likely to make people ignore it. Please click "Edit" and "Go Advanced" and give your thread a more appropriate title, such as "Can I have WinXP and *nix both on my HDD?" and people will be more inclined to help.
Also, since people volunteer their time to offer help to other members, nobody's problem is really "urgent" to anyone but themselves. Kindly review the LQ Rules here: http://www.linuxquestions.org/linux/rules.html
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As to your question, the answer is YES -- you can install more than one OS on your hard drive, and dual-boot it if you like. This subject has been covered to a great extent in many many threads here on LQ, and a quick search for the term "dual boot" should provide you much info to get you started.
If you have further specific questions to ask about your setup, or run into stuff you don't understand, please feel free to expand upon the situation in detail, and we will do our best to help you out.