Installing Win98SE has been a breeze for me, but I wanted to make a thread with all the drivers I've used to help others.

First thing I did, though, was going in the BIOS and disabling everything.
I didn't need Ethernet, Wi-Fi or anything else: only audio, video, PCMCIA (for my CF card) and USB.
I also disabled speedstep because it's known to create problems with some games.

To install Windows I just created a bootable USB with MSDOS, copied the Windows98 files over and booted off it.
I then proceeded to format the hard disk, transfer the system to it with "sys D:" (change the letter accordingly) and copy all the content from the USB to the hard disk.
Rebooted and then there's the first choice you have to make: ACPI or APM.

I've tried both (for reasons explained later) and they are honestly the same.
I think it runs just a little bit better in APM.

Either way, to install with ACPI just run "setup".
To install with APM run "setup /p i".

Installation is super fast from the hard disk and then you can proceed to install the drivers in the order I've given them, with some care:

1. Chipset: After installing, on the reboot, it will ask for extra files. You can find them in the same folder of the installer
2. USB2.0: You don't have to install the whole NUSB3.6. I didn't care for flash drives as I use CFs, so just point the Universal Serial Bus device with the exclamation point in the Device Manager to the folder and it will install the USB2.0 stack
3. GPU: Same as chipset: after installing and rebooting it will ask for extra files: those are already there in the folder of the installer. If you don't plan on using an external monitor, go into the Device Manager and disable the second GPU which points at the external monitor. It will save you some hassle with DirectX later.
4. Directx 7.0a: For reasons unknown, the GPU needs Directx 7.0 to have D3D acceleration, despite it being a DX6 card. You can download and install DX7 from Phil's Computer Lab website here: https://www.philscomputerlab.com/directx.html – Instead, if you want to use the external monitor as well, you'll have to use Directx8.1 (don't ask)
5. Audio: Those are the drivers from Dell's own website and despite saying they are for WindowsXP, the .INF states "Chicago" which means that it's compatible with Win9x. If you try to install them they won't work, you have to right click the audio device in Device Manager, Update Drivers and choose manually, then "Have Disk", point it to the folder, Windows will complain, ignore it, install it and reboot. Job done.
6. PCMCIA: even though Win98 already has the drivers, those are newer and they gave me less issues. To install them just go to Device Manager under PCMCIA and make sure to update *all* the devices there by pointing it to the folder

Those drivers are the most updated I could find around and they work alright.

Now, for the ugly part... all the devices IRQ are amassed at IRQ10.
There is no way around it and the BIOS, even updated to the last version, is a complete and total disgrace as it has no option whatsoever for assigning IRQs manually to PCI lanes.
I've tried everything I could and there was nothing I could do, you'll have to live with it.

Hopefully this helps!

EDIT: another small note.
You can enable Speedstep in the BIOS and it will work, but I prefer to keep it disabled to avoid issues.
This means that your CPU will be stuck at 600Mhz (6x multiplier) at the lowest P state.
It's not an issue for me and the games I played, but I've found out that by using CPUSPD in the Autoexec.bat I can bump the multiplier up to 10x and go to 1Ghz while retaining the lowest P state!
That's awesome because it means that the laptop will run cooler and eat less battery.
If you need lower speed you can obviously lower the multiplier as well if some game complains.
The syntax is "cpuspd m10" (change "10" with the multiplier you want).

You can get CPUSPD here: CpuSpd - A Hardware Based CPU Speed Control Utility for DOS/Win9X Retro Gaming