sql 1390c error while installing DB2 8.1 on windows 7

[niroopa]

HI guyz...
During the DB2 8.1 installation, i got an error saying that Db2instance is not defined or invalid...

The error dialog box shows as :
[ DB29501E DB2 has detected an inconsistent environment. Please investigate the following:
"DB2Instanc e:-2029059916"]

i have checked the environment variable 'DB2INSTANCE, initially it was not set, by entering into the MYcomputer-> Properties->Environment Variables, updated the
'DB2INSTANCE' variable...but still getting the same error.

so please anyone could help me out of this error.

Operating System : windows7 Ultimate(32-bit)

Thanks in Advance..