Sorry.
Well, I think I will stay with the 2+2 Gigs solution. It will surely be good for the next 2 years.
After that, I will buy a new laptop anyway. And that will have DDR3 slots, so I won't be able to use my old DDR2 rams, as it will slow down the DDR3-s as well. 

Confirmed: 8gb of ram on inspiron 1501 1.6ghz AMD Tourion Duo 64bit with XP Pro 64

I couldn't justify the cost of upgrading to a 64-bit OS, so I just put 2+2 GB Hynix DDR2 PC2-6400 in, and Vista 32-bit Basic sees just 2.686 GB, less than .3 GB better than what BFunc got with 2.5 GB, but it works fine.  FWIW, an SSD is a better upgrade than memory, with only 1GB of memory and the SSD this thing is fast enough.  Kingston V100+ bundle.

I'm another user with 2 2GB 800 MHz memory sticks in the Inspiron 1501. I will keep my eyes open, and if more people are running 8GB, I may upgrade to that in the future. I'm running XP Pro SP3, and seeing 2.6 GB. I have Hynix and Micron RAM. My wife's Latitude D620 didn't like the Hynix, so I'm using both sticks of that in my 1501. Her D620 has 2 2GB 800 MHz module of Micron RAM.

I confirmed 4gb will work as well. I was thrown off when I visited this website:

www.ecotekmemory.com/.../certified-compatible-for-dell-inspiron-1501-ddr-2-pc2-4200-533mhz-200-pin.html

As it said that the inspiron 1501 only supports up to 2gb. I emailed them about what we have been talking about, and they actually confirmed that it does in fact take up to 8gb, and they will be updating their site shortly to reflect this.

I was going to order cus they had a great deal on 2 1gb at 24.99, but I am going to wait for them to have 2gb modules.

Can't wait to have 4gb in my inspiron 1501 with windows 7 64 bit. I should be flying!.

Thanks for all the info.

I wonder if anyone has tried 16GB yet...

maximum per slot in that machine is 2GB

besides I am pretty sure no one manufactured 8GB Modules for laptops in 533mhz ddr2

<ADMIN NOTE: Profanity removed as per TOU> Clown he said he will be installing Windows 7 64 Bit,, what part of 64 bit did you not comprehend ?

The chipset is reported to handle up to 8GB. I haven't tried it, and I know the max memory does depend on the motherboard as well. Even with 4GB, it'll only "see" 2.6 GB of RAM with a 32 bit OS. The rest of the RAM will test OK in BIOS. IMO, having the extra 620 MB available in dual channel mode is worth the price of two 2GB sticks.

I believe the board can support a bus speed of 800 MHz. I'm running 800 MHz DDR2 and a TL-68, which has an 800 MHz bus (well, 200 MHz x 4 read/writes per clock cycle) and if it's running the bus slower, I haven't noticed. I guess it's time to bench it and see. It's certainly given me no problems with the faster memory at all, so if you can't find 533 MHz, just go up to 800 MHz (PC6400) and you'll be fine.

BTW, I'm running Hynix RAM. The machine also likes Crucial and Kingston as well.

I know it's been forever since you posted this, but I was wondering if you've done any other upgrades; namely, have you moved to 7 yet? I ask because it's what I'm currently running (64-bit), and I want this to be the last series of upgrades I need to do, at least for a long while. I've read on Crucial's site that Win 7 64-bit will recognize up to 192GB of RAM.I know they don't yet have a way of fitting that amount into to DDRII slots, but I want to know what the ABSOLUTE MAX I can run is. Thanks!