Why are you still using Windows 98?

Find a dx8.1 setup file. Run it. Here I have a file named directx_apr2006_redist.exe, but I'm not 100% sure that's the one I installed in the virtual machine, and have no idea what version of directx that is.
WTF do you need flash for, anyway?

>>286
Probably to play old games.

>>286

This. Windows 98 is dead in the water, practically unusable if you're trying to do anything normal (by today's standards) with it.

>>287

If you want to run old games that aren't compatible with Win Vista/7/8, just use the compatibility options that let you run a game as a certain version of Windows. It worked for me when I tried running Half Life 1 on Win7. If you want to run DOS games (i.e. DOOM), download DOSBox (DOS emulator).

And I wouldn't even bother trying to get Flash working. Any animation you view nowadays will require a fairly recent version of Flash, which you're NOT going to get on Windows 98, and even if you did find a way to install it, have fun trying to run it with your endless BSODs.

tl;dr upgrade your OS.

>>290
Compatibility mode doesn't work for most of the games I tried, although it might be different in the 32-bit version of Windows.

I'm curious as to what OP needs Flash for. He can't possibly use Windows 98 as his main OS.

>>292

>64-bit Windows

That's likely where OP's problem lies if he initially tried running old games with Win Vista/7/8. Old games were made long before 64-bit architechture was adopted for domestic machines.

>>293
The compatibility modes should go back to 32-bit (or even 16-bit, occasionally). I read a blog from one of the guys at Microsoft who worked on compatibility, and they make sure old hack-y 16-bit VB programs work, since businesses still use them.

>>333
Nope. There's no 16-bit compatibility at all in Windows 7.