What is type of RAM in your old system. DDR1 or DDR3
If DDR3 and = or > 2 GB then you can install W7 or W8.1 even of old configuration.
If DDR1, then, if your system can handle 2 GB of RAM then you can install W7
The older system like P!V, has DDR1 type of RAM and mostly 512 GB or the max 1GB, which is not sufficient to run W7 atleast 2GB RAM is required for smooth working. If interested in converting it, just contact a computer technician, though the availability of new DDR1 RAM of 1 GB is not good