You can do a decent 'temporary' job for a visor sticker using an ink jet printer, but for a proper long-lasting job you'll want to have them professionally printed on vinyl decals. See here for good resources on visor stickers and helmet painting:
http://www.teamjuicyracing.com/forum...ead.php?t=1280
If you just want to do a temp job, then:
1. Print out your visor sticker in high quality color mode on a full page single label piece of paper (avery etc.) Do a whole bunch of test prints on regular paper first to make sure you get it right.
2. Cut it out and trim it.
3. Get some high-gloss polyurethane spray paint, and make multiple light coats, allowing sufficient time to dry between coats. The paper will absorb the first few coats completely, so be patient and don't over spray - the gloss and the proper effect will show soon enough. When it's glossy enough, stop, and let it dry properly before you apply.
The downside to the hand-made labels are that they tend to run when they get wet, and that the adhesives in the paper labels become quite messy to remove when you decide to change or remove the strip.
Good luck.
S