Any monitor can be calibrated, however LCD monitors with TN panels are rather difficult to do so because they are all 6-bit monitors meaning they a can only produce 256k true colors. Thru a process called dithering (blending of colors) the remaining 16 million colors can be reproduced; at least according to the manufacturer. For the average user TN panels are good enough. For professional photo work, it's not recommended since colors tend to be inaccurate even after calibration.
You can purchase hardware color calibration (colorimeter) like the inexpensive Spyder 2 for around $70. But colorimeters can cost more than $300; the good ones usually do since they generally create more accurate color profiles.
Go to the following link which helps you manually calibrate your monitor. It's not as accurate as a colorimeter, but it's free and better than nothing:
http://www.lagom.nl/lcd-test/