can i install 32-bit os to 64-bit

Hi amsingh,

The Inspiron 1520 is not tested with Windows 7; However, you can try installing the driver (windows Vista) in the compatibility mode.

Follow the steps below to install in compatibility mode

Right Click the driver installation file and select Properties/Compatibility Tab > check the box run this program in compatibility mode, Select the appropriate options.

With 4G of RAM (you won't see all of it because of hardware limitations) you are better off with the 32-bit version of Windows 7.  You can run the 64-bit version but will get better memory utilization and performance with the smaller kernel footprint of the 32-bit version.
Because of the chipset in the system, you won't see all 4G of RAM even with a 64-bit version of the OS - the system is too old for that.

The processor has a 64 Bit instruction set:

http://ark.intel.com/products/29759/Intel-Core2-Duo-Processor-T7100-2M-Cache-1_80-GHz-800-MHz-FSB 

You can install Windows 7 64 Bit, to do so see Windows Reinstallation Guide/A Clean install of Windows 7:

http://philipyip.wordpress.com/dell-community-forums/

Use the following drivers:

http://philipyip.wordpress.com/unofficial-driver-sets/inspiron-laptops-windows-7/inspiron-1520-windows-7-64-bit/ 

http://philipyip.wordpress.com/unofficial-driver-sets/inspiron-laptops-windows-7/inspiron-1520-windows-7-32-bit/ 

As mentioned the system is limited to 4 GB of RAM so there will be little benefit to installing 64 Bit Windows 7. In addition as you currently have 2 GB of RAM, you would have worse performance on a 64 Bit OS opposed to a 32 Bit OS. However RAM is easily upgradable and you may upgrade to 4 GB using the part here:

http://www.crucial.com/upgrade/Dell-memory/Inspiron+Laptops%2FNotebooks/Inspiron+1520-upgrades.html

No point in installing 64-bit OS on a system with 2GB RAM.

Still no point - your system won't see all 4G even with a 64-bit OS because of the hardware (chipset).

what if i upgrade my ram to 4GB?