I invented and published it back in 2002. There's plenty of proof. I'm wondering 1. if it's a good idea just to keep someone else from patenting my invention, 2. if it's even worth trying (what would I stand to gain) and 3. how expensive it would be.
At least under US law, no.
35 USC 102:
A person shall be entitled to a patent unless—
the claimed invention was patented, described in a printed publication, or in public use, on sale, or otherwise available to the public before the effective filing date of the claimed invention;
Disclosures made 1 year or less before the effective filing date of the claimed invention.—A disclosure made 1 year or less before the effective filing date of a claimed invention shall not be prior art to the claimed invention under subsection (a)(1) if [...]
[section numbers and such removed -- see 35 USC §102 if in doubt about precise contents/wording]
So, to make a long story short, under the right conditions, you have up to one year after publishing and/or selling the invention to apply for the patent, but after that one year grace period, you're pretty much out of luck.
Although laws obviously vary by country, I'd be a little bit surprised to see anybody accept a patent application on something you published in ~14 years ago.