the 600 series has been considered one of the best platforms IBM came up with... thin, light, all around good laptop..
You didnt mention which model you have, (look at the label on the bottom) It is probably a 2645-51U, which is a plain 266Mhz, 32MB, CDROM equipped 600. It may be a -4xU(which is just a little lower entry level configuration, 200/233/266MHz, with zero RAM). To get the specifics of what you have, click on this link:
http://www-307.ibm.com/pc/support/site. ... lang=en_US
where it says Quick Path on the right side, type in your model number(2645-xxx) and it'll tell you how your model was -originally- equipped. Plus, it'll give you a bunch of links to drivers, documents and the like.
ok, first... the two best upgrades you can do fairly cheap are, max out the RAM,(288MB max = two 128's plus the 32 on board) or at least up it to at least 128MB.. that would be a PC66 speed 32MB and a 64MB RAM , plus the 32MB installed on the motherboard. If you already have more than that, all the better.. Here's a PC66 SODIMM link.
http://search.ebay.com/search/search.dl ... C66+SODIMM
Pay no attention to those that say PC100 or -133 memory will work... trust me, it wont. Just avoid PC100 and PC133 speed memory.
Second, upgrade the CPU. If its a 266, you can swap the cpu with a 300, 333, 366 or 400MHz processor. 400's are kinda hard to find and a little pricey, while 366's are cheap. The swaps are very easy. The 600's will ONLY take an MMC1 form, (or MMC-1). Even if it says Dell, Gateway, etc, it's ok, but it must be an MMC1.
http://search.ebay.com/search/search.dl ... Card+-card
24 speed CDROM's go pretty cheap on eBay(usually $10-$15). You can even find DVD drives for $40-$50, tho the playback is a litle choppy. Not really distracting, but noticable.
http://search.ebay.com/search/search.dl ... +600+CDROM
As for WiFi, just about any 802.11b or .g PCMCIA card will work. I use D-Link and Linksys, tho I also have a couple no-name .b cards that work ok too.
Batteries, sorry to say, aren't really cheap, but they are coming down..
http://search.ebay.com/search/search.dl ... 00+battery
Good luck with it. Your girlfriend will love using it.
TJ