Windows 7 doesn't seem to support infra-red very well.
In your case the problem is doubled because the 64-bits mean you can't use older drivers.
However, if you still have around an available XP/Vista driver that does what you want, it might still work in XP Mode (which works in 32-bits).
See if the following article helps in XP Mode :
How to configure your computer for infrared communication in Windows XP
If this advice doesn't work for you, it would help to know how do you connect the irDA adapter (USB?), and whether it is recognized by Win7, or if Device Manager can find it a driver in either normal or XP modes. Also, what was the last computer/Windows-version on which the device used to work, and whether you still have the installation media.
These products might help :
Serial Port Mapper
Map any serial ports to virtual serial port.
Virtual COM Port Drivers
Cause the USB device to appear as an additional COM port.
If you manage to advance a bit, the following article might also help :
How to Set a COM Port for an Infrared Adaptor.
Some people have solved the problem hardware-wise by buying Polar adapters.
The thread Drivers for USB on windows 7 says :
Polar IR Interface for USB port
Polar IR interface for USB
(white) is supported for Windows 98,
Me, 2000 and XP. It is not supported
for Windows Vista and 7. Some tests
indicate, however, that Polar IR
interface for USB drivers can be
installed to Windows Vista and 7
running on a 32-bit hardware. The
infrared will not install on a 64-bit
Vista/7 because the drivers are not
Polar IR Interface (RS232 port)
Polar IR Interface (black
for RS232 port) is not supported for
Windows Vista and 7. In our tests,
however, Polar IR Interface has worked
well on both 32- and 64-bit Windows
Vista and 7. As this is an RS232
device no drivers are needed. The
system takes care of communication.
In case there is no serial port on the
computer and you want to connect the
device to the USB port, you need a
third-party serial-to-USB adapter with
Windows Vista/7 support. Polar does
not offer such an adapter.
Polar IrDA USB Adapter
Is supported for Windows 98SE/ME/2000/XP.
Polar IrDA USB Adapter is supported for Windows
98SE/ME/2000/XP 32/64-bit, Vista and 7
32/64-bit. Please make sure you have
updated Microsoft Service Pack before
installation. Latest drivers are
available in here: Polar IrDA USB