Hi anish,
you need to specify power requirement, something like
1.5A @ 12VDC and 0.5A @ 5V.
getting 5V can be done using 7805 regulator. the excess voltage
(assuming battery voltage is in 12-15V range, it could be 12-5=7V or 15-5=10V) and required current (say 0.5A) will create some heat.
so 7V*0.5A=3.5W or 10V*0.5A=5W. This means that you probably need heatsink for this regulator. 5V is used for electronics of the drive and probably has to meet TTL standard for 5V power source (4.75-5.25V) which is easily done with the good old 7805.
12V rail is used to power motors in the drive and it doesn't have to be quite so precise as 5V. You might want to try taking it directly from car battery or maybe drop it a bit with two diodes for example since the average battery voltage is usually a bit higher than 12 anyway.
diodes would have to meet current requirement of the drive's 12V side.
I mentioned 1.5A as an example. in such case it would be good idea to forget 1A diodes such as 1N4001-1N4007 and go for something bigger such as 3A versions 1N5401-1N5407.