I have a Dell Inspiron N5010 with Ubuntu 10.04 installed , and i canot get the inbuilt or any other microphone to work on it . Is it some driver issue ?
Most probably it is the driver issue (it's a single driver, called Alsa, and is part of the Linux kernel).
The best you can do is get a Ubuntu 11.04 LiveUSB (see http://www.ubuntu.com/desktop/get-ubuntu/download section 2) and boot your computer. If the mic now works, then the latest Linux kernel 2.6.38 (with Alsa 1.0.24) fixes your issue, and you simply need to upgrade your Linux.
If you do not want to upgrade yet, you can simply install the Alsa driver 1.0.24 onto Ubuntu 10.04, according to the instructions at https://wiki.ubuntu.com/Audio/InstallingLinuxAlsaDriverModules (you use a PPA repository). This is mostly for testing, and when you get an Ubuntu 10.04 kernel update, your mic might not work until the corresponding driver in the PPA gets updated.