I'll answer what I can..
1. You're gonna have to ask a Dell CSR about this one.
2. Gonna reverse your question to why a 4000 instead of a 5000e here . For your uses, I'd say the 4000 should suit you fine. You said you'd like a 14" screen... The 4000 meets that requirement. The 4000 also weighs in at 5.2 lbs. to 6.2 lbs. and is 1.47" thin. 5000 is 7.2 to 7.5 and is 1.6". Also if you look closely at the 4000 series, you'll notice it has that dual touchpad/"ereaser head" mouse. The 5000 doesn't. As for style, the 4000 has some of those quick acess multimedia keys on top. The 5000 is just your standard more "professional looking" notebook.
3. As you already have somewhat stated, The 5000e does offer a 15 inch display. As posted in my previous post. Ask yourself this question... "Will I be actually using 1600x1200 on a 15 inch screen?" Take the dot-pitch into consideration too. I myself will probably most likely be using 1024x768 on my lappy. For reference, SXGA+ can support up to 1400x1050. XGA supports up to 1024x768. I say go with SXGA+ gives that extra 87% pixel space for those just in case moments (ie web design).
4. If you know how to fiddle with the URL, you can have any type of system. If you notice on URL. Dell basically gives you your notebook options via the "e-value" code. Here is an example.
http://commerce.us.dell.com/dellstore/config.asp?customer_id=19&keycode=6v918&order_code=
5000rl&x=0&y=0&dgvsite_id=msn-promo
Notice when you visit Dell's page via the MSN promo link, only SXGA+ displays are available. Change that to:
http://commerce.us.dell.com/dellstore/config.asp?customer_id=19&keycode=6v920&order_code=
5000rh&x=0&y=0&dgvsite_id=msn-promo
Now you have the UXGA displays available! The e-value codes are genrally next to the "printable summary" tab. Find the codes you want and enter them to get your desired system. Just keep the selections in the Home & Home Office section to make your 20% valid. Although it is possible to buy systems at the lower acedemic price and have the MSN Promo text still visible by fiddling with the URL, keep in mind in the terms of the 20% rebate promo, it says it only applies to the Home section.
As for your selection of a Celeron 600, I'd get a Pentium III 600 instead. The PIIIs have speedstep which will preserve your battery life (drops to 1.35 volts in speedstep). The Celeron 600 doesn't have this feature so it sticks at a constant 1.6v.
5. Hopefully Bluetooth will come on to be the standard. If that's the case, I'll be getting one too.
You might want to just consider getting an aftermarket NIC PC Card as it's probably cheaper than what Dell is charging if you get the 5000e. You already have a internal 56K modem there... Although it's probably a winmodem/softmodem.
For the 4000 model might as well get the integrated one as it is for a reasonable price... Saves you a PC Card slot too.
6. Go with 16MB. You said you plan to play some racing games and most current ones at least use some sort of 3D API. If you stick with 8MB, you'll be limited to a 64-bit memory bus bandwidth. Not a pretty sight for gaming. With 16MB, you get the full 128-bit memory bandwidth. Desktop should be fine however even with 8MB.
7. Since you have a copy of Win2K Pro. Why not ask Dell if you can have the system without an OS? Might not happen but doesn't hurt to try!
For WinME, there are some troubles with it... Some Dell users have said that ACPI doesn't work properly in WinME. If ACPI is important to you, stick with W98SE.
On my desktop system W2K usually eats around 140MB of memory, I'd go with at least 192MB if you plan to use that OS. Drivers and utilities for Win9x/ME/2K can be found on Dell's site.
8. Since you said you'll be only using it for about 1-2 hours a day. One battery is more than enough.
9. Complete care is basically a type of insurance for your notebook. Just don't do something stupid with your notebook and you'll be fine. But if you're one of those people that might accidently damage a notebook (e.g. run over it with a car because you forgot to pick it up from the ground), get complete care. Also... from Dell's site:
Complete Care is not available in California, New York, North Carolina, Virginia, Vermont or New Mexico and Florida.
CompleteCare covers all accidental damage except fire damage and also excludes theft, loss and damage due to intentional damage. CompleteCare is currently not available in all states.
Down to the nitty gritty... Will you get a lot more power from the 5000e? probably not too much. The 4000 uses a 53WHr while the 5000e uses a 59WHr. Better screen? hmm... 14.1 inch (max 1024x768 res) on 4000 and 15 inch on 5000e. You decide your resolution needs.