If the E-510 you purchased is not modified for IR work, it may not be the appropriate tool. Digital cameras these days come with UV/IR blockers over their sensors to keep colors true (UV/IR sensitivity can throw off greens and purples on sensors). This blocker greatly reduces the IR sensitivity of the sensor. It doesn't completely reduce it, but it does lower it to a high enough degree that infrared capture with an IR pass filter on the lens is typically done at very long shutter speeds even in bright sunlight (say, 30s to a minute).

You may want to look into getting the camera converted (or returning it and purchasing one that's already converted. Conversion involves removing the IR/UV blocking filter over the sensor and replacing it with an IR filter or clear glass that allows all spectrums through. (See the lifepixel website). Whether you use a converted camera or not will have an impact on which settings you can use, ISO or otherwise.

To use an IR filter, you usually screw it onto the front of your lens. The filter should be the same size or larger than the filter thread on the lens (if it's larger, you use a step-up ring to make everything fit). The filter size of the lens should be written on it, with the diameter symbol (e.g., ∅58mm).

From reading an Introduction to Infrared Reflectology article, it also sounds as if you probably need to be in a dark room, and using only IR lamps on the painting.