I have a Dell Pentium 3 for a D820 I also have a few other Dell's that need upgrading to p4...what can I do to the default system set up to support the new p4 from a p3? I will do anything....

P4 what, what does its lid stated, P/n FULL
only P4HT works here, not P4 older than 2003 sold.

so let me guess, you didnt ask DELL first.
for a list of processors this motherboard supports.
and the other processor (unnamed) works? (2nd shoe drops)
Didnt upgrade the BIOS first, so it can support a larger list
of qualified Dell Processors?
RTC coin cell fresh, not dead,? 2.9vdc minimum.
Dead BIOS is wrong processor, or bad RAM.
assumes good monitor and PSU.
and both fans spin, PSU and CPU.
not running CPU nake,d no heat sink and fan is (super bad choice)

steps not taken.
1: ask dell first. (dah factor 1, we are not dell)
2: tell Dell what P4, it is (it has a full number on top that you forgot to state.)
3: upgrade bios if dell tells you it does this version of P4, and id does not? then back to P4 store for correct P4 only DELL told you can work.
"called the qualified Processor list" only dell has. ok.?
4: install it correctly, with heat sink, thermal grease and fan.

Your PC Needs A Bios Upgrade !

Consult The Manual For Your Dell PC !

https://www.driverscape.com/manufacturers/kobian/laptops-desktops/pig31t/8059

Yes you can upgrade it with Pentium 4.It will be working fine with P4.
So you can do it.

You cannot upgrade from a Pentium III to a Pentium 4 without replacing the motherboard.

To be honest, the Inspiron 1100 is probably not worth the effort and cost to upgrade
The fast is proc is a 2.4 GHz Pentium 4 CPU, max ram 1GB of RAM,
You can find several dell portables below $500
http://www.dell.com/us/en/business/notebooks/vostronb/ct.aspx?refid=vostronb&s=bsd&cs=04
http://www.dell.com/us/en/home/laptops_great_deals/fs.aspx?refid=laptops_great_deals&s=dhs&cs=19

you will need a new p4 motherboard and processor+(heatsink fan).your memory might still work,depends if its the same or not.
make sure your video and sound card will work with new board,or get a board with onboard sound and video.

I'm not sure about the CPU upgrade--these generally are hard to determine and this is complicated by the fact that Pentium III processors are no longer made, I would say that you could go on e-Bay and find one there (should be cheap) and try it.
An easier way to get a little more speed is to bring the memory up to the maximum the laptop will hold. (In your case 512 MB). That and set the paging file to allow the system to determine the size needed (Unless your system has Linux installed). Any further upgrades on an older system like yours are usually just a waste of money.

The board may not be able to support that processor. Check out the board specs to make sure it can use the P4 and make sure the sockets are the same.

To upgrade from pentium 3 to P4 you have to change alot of the hardware.

You need a NEW P4 Socket mPGA 475 Motherboard.
New DDR RAM
New 478 PIN Processor.

You can use the old CD rom and Hard drive and any other PCI card but You Need the Mentioned Hardware to Upgarde.