Remotes are cheap enough, in the $35 neighborhood through someplace like 'keylessentryremote.com' or some such (I can't remember where I bought my extras, maybe through eBay), and darned nice to have. The gouge comes in when the dealer has to program them... something like $40-80. I kissed up to my dealer and got them to do it for free.
But mine's a 2000, and I think '98's are different because the ignition systems are the older style? Scottish would know.
There’s no sensor on a P80 that detects window position.
Unless you have the extremely rare optional glass breakage
sensor, I’d recommend leaving at least ONE of the windows
down whenever messing about with any weird lock issue.
( The experience of getting locked out is never optimal
and you never know what a rogue alarm will do...)