Though you haven't explicitly said about Wubi install, I guess you are asking about Wubi installation of Ubuntu.
The short answer to your question is, Yes, If your CPU can support 64bit computing. In recent days, almost all CPU support 64bit OS. So, your chance is very high.
If your CPU support 64bit OS, then of course you can install another instance of 32bit Ubuntu inside your Windows. All you have to do is, Install the second instance of Ubuntu on a separate partition than the one, where you installed 64bit Ubuntu. That means, if you installed 64bit Ubuntu of
D: drive, You can't install another instance of Ubuntu on the drive
D:, so choose another partition for it.
After you installed 32bit Ubuntu, you should have three entries in Windows Boot Manager. The First one is "Windows" and the second and third one will be labeled "ubuntu". The first "ubuntu" entry is the 64bit Ubuntu (which you installed first) and the second one (the third entry) is 32bit Ubuntu , you installed later.
To make an Ubuntu entry as Default boot:
Boot to the Windows
Right Click on the Computer icon, either in the start menu or in the Desktop and select Properties.
In the Properties Window, in the left blue side bar, there will be four link. Select the link saying "Advanced System Settings".
In the new window, Select "Advanced" tab and in the "Startup and Recovery" section, click on the "Settings" button.
Under "System startup" select an Ubuntu entry from the dropdown menu. Close all the windows.