When fans wear out, they tend to run slowly or stop intermittently. It's a good thing that you are considering getting a new fan. (make sure you use some good thermal paste if you replace the heatsink as well as the fan.)

As for using the computer until then...Make sure the heatsink is clear of dust and see if you can open the side of your computer case and place a larger fan directed into the case. It may cool the CPU and other components enough to run the computer. You probably want to check the temperatures on your CPU consistenly though as Intel CPUs should not exceed 71° C, as written in the Intel specification for Prescott series CPUs.

If you have an Intel motherboard, you can install the Intel Active Monitor ( http://www.intel.com/design/motherbd/active.htm ) to get a realtime view of CPU/system temperatures and power supply readings.