Returning to Win98 or maybe 95 on old machine/ mobile broadband andW98

I have a 1999 Fujitsu with 512 mb upper limit for RAM and a 1.3 ghz
CPU. I have spent time and money stretching it with a bigger hard
drive, more USB ports, a graphics card and doubling the RAM from 256
mb, and also by trying many Linux distros (including XFCE versions),
along with XP, W2K and even Vista Home Basic. Its performance isn't
atrocious, but it does of course draw windows and work with the
internet not so fluidly as my Vista-cum-Windows 7 laptop and my
netbook. I'm thinking of reverting the purpose of the machine back to
why I bought it secondhand, just to write a novel on, and I use the
Wordpad derivative Jarte after a year of trying OpenOffice.

I stupidly gave a Windows 98SE CD away with a laptop I sold but might
buy another off eBay, though I do have a Windows 95 somewhere. I
didn't see any 98 isos on 'certain sites' but would feel more
comfortable with my own CD anyway unless anyone has any
recommendations.

Would I _notice_ a performance improvement if running an OS from the
era the machine was built, or would it still be glitchy in the same
way? I have seen Windows 98 in action fairly recently, but that was
on a 200mhz and a 500mhz machine with 80mb and 128mb RAM, so I've
ignored my impression.

I have a 240 gb hard drive, with a 20gb one sitting in a drawer.
Apparently the 240gb will be of no use to 98 or 95, but is that simply
a case of setting up a partition smaller than 80gb or whatever to get
it to use Windows 95 or 98, or is it going to have to be that the
240gb hd sits in the drawer for now?

My other, not immediately viable option is to buy a new motherboard,
CPU and RAM and put all this in the Fujitsu's case with its psu etc,
but I'm a bit wary of how that might turn out, envisioning explosions,
flames and so on... For now, and in this post, it's the 95/98
question I'm interested in.

Lastly, has anyone here successfully set up a mobile broadband dongle
with Windows 98, maybe as a dial-up connection, or is the lack of 98
drivers a permanent scuppering of this? I'm not super-bothered, as
it'd be healthy to prevent myself getting online with this machine.

Thanks in advance for any advice.