What do I do with two prong plugs in my house, when my fuse box is grounded?
It may already be grounded.  Back in the day, it was common to use either metal conduit or metal-armored cable, which provides a ground path.
If you only need human-safety protection and not equipment protection (e.g. from ESD), then you can convert 2-prong receptacles to 3-prong by providing GFCI protection.  You must add a sticker &quot;No Equipment Ground&quot;, and if the GFCI device is somewhere else, also &quot;GFCI Protected&quot;.
If one is clever, and if one is poor it pays to be clever, then one can get by with a single GFCI device per circuit.  The labeling is still required.
Lastly, it is legal to retrofit just a ground wire to a box that has no ground.  The ground wire must be the proper size for the circuit, and must go back to either a) the panel, b) a junction box with metal conduit going back to the panel, c) a junction box with a big enough ground wire going back to the panel, or d) the bare copper Grounding Electrode System wires.