Even after uninstalling the Websphere i am unable to install the Websphere in the same location , it's required for our project but it's displaying while installing please specify the different folder, already exists it's displaying.. can any body help me out on this? i hope it may be storing the details anywhere in files or some where. I checked in vpd.properties no use..

One more thing is difference between the Network Deployment & clustering? in WAS.

Can anybody help me out how to create multiple JVM's? is it possible in Standalone? 

#1 . If your uninstallation is successful .. then delete all websphere related directories before you re-install

#2. WAS ND provides options to create clusters.

#3. standalone is one jvm that stands alone . you need to create a DMGR and federate a node to create multiple JVMs.
While you create the profiles .. lookout for 'CELL' profile option.

If we need to create a DMGR and federate a node to create multiple JVMs. Then we need to go for Network Deployment only right?

Yes!