I have installed ubuntu 11.10 to my dell notebook. I am very satisfied so far. how many years will it be supported from ubuntu. or should I install long term support version?
Non LTS versions of Ubuntu are supported for 18 months from release, so 11.10 will be supported until April 2013. See the ubuntu releases page for details of the different releases and their support periods.
If you were to install the current LTS, 10.04, then desktop support for that release would also end in April 2013, so that doesn't help. Though 10.04 is likely to be that much more stable at this point as there has been longer to debug it.
The next LTS will be released in April 2012 and will be supported for 5 years on the desktop.
Overall my advice to you would be to stick with 11.10 for now, and once 12.04 LTS has been released upgrade to that. The last few upgrades have been very reliable and simple for me. After the upgrade you can stick with 12.04 for up to five years and still get updates.
Until April 2013, so in total one year and a half. Here is a table with all the support periods.