Did you update to service pack 2 w/ XP when you installed it and did you let the machine update automatically? Did you download and update Java? Did you upgrade WMP to WMP 10? It sounds like you are having a problem with explorer; if certain images and video (streaming) do no show up on html pages and you have updated Java and Flash you are having a general problem with explorer. [ FYI, your old win98 PC is going to work the same it did when you unplugged it; the problem is with the software in your new winXP machine not the HTML pages you are visiting...]
If it was a driver problem, which you say it is not, odds are the computer would flat out crash when it attempted to process any file that created a conflict with the OS and drivers for your graphics card, so if you can watch the video independently with no problems, i.e. an avi, wmv, mpeg etc. but not on a web page it is problem with your software.
Solutions:
(1) update to service pack 2 + security updates & WMV update
(2) update Java
(3) for the f*ck of it try using Mozilla instead, odds are this won't fix your problem but I don't know how independently mozilla firefox operates from explorer.
(4) Bite the bullet and call the evil empire and ask them kindly, more soup please
j/k. You can call MS tech. support and link your PC to a tech. support rep. and they will diagnose the problem and fix it for you.
IF you bought your XP you have 2 free phone calls to them for help, but use them wisely because after that it is like $50+ for tech support (they really bend you over so be forewarned.)
(5) Shareware problem solve: download a program such as TuneUp Utilities 2008 use it for free for 30 days and let an app. try to fix the problem for you ( I recommend TuneUp 2008 cause I use it and feel it gets good results.)
(6) Clean install (run and hide the children!!!) If it was me, and I did all of those things and still got zip I would do a clean install before a gave Microsoft a nickel of my money, but that’s me. There is a strong chance XP just plain out f*cked up when it was installing, it happens, even a MS tech rep. once admitted it to me. If this is the case your dead in the water if you don't do a clean install because the problem is unfixable and the tech rep won't even be able to ID what the hell is going wrong, and even if he/she could there would be nothing that could be done
but a clean install. Since it is brand spanking new PC a clean install won't be that much of a ball buster because you haven't really done anything yet, and you should still have all your install disks and drivers so it is just a matter of install time.
Hoped that helped, if you provide more info more solutions will arise