(warning: long post)
Well... here we go again.
I decided to do some testing this weekend. My current slave HD has 40GB (it will be replaced by that 120GB one), it only had about hdb1 = 38GB for Ubuntu 6.06 and hdb2 = 2GB for Swap. This partitioning was made by the Ubuntu installer.
My RAM memory is of 1GB (was 0.5GB until a few days ago). My master HD was (until hours ago...) of 80GB FAT32 formated with Windows XP on it.
OK... I take a Live-CD and do some mess... Aproximate figures for new partition table:
hdb1 = 9GB ext3 for files
hdb5 = 1GB swap (yes, I don't even need this much)
hdb6 = 10GB reiserfs
hdb7 = 10GB ext3
hdb8 = 10GB ext3
OK, let's boot again. Zenwalk 4.0 CD on the drive, install it to hdb6. I let it install LILO on the MBR (master boot record), since it doesn't offer GRUB as an alternative. No problem with this. Install went fine, LILO automaticaly recognized Windows on hda1.
Found Zenwalk to be very, very fast and without fussy or choosy things. Very good to my taste. And having a very small repository means a nice oportunity to learn how to install stuff "by hand", although it brings Xfce and basic stuff with it, but only the minimum needed. It also lacks some GUIs for configuring stuff, so I also have the oportunity to learn configure my system a harder (and better!) way.
OK, back to life.
Ubuntu 6.06 live-CD on the drive, let's boot it up and install on hdb7. Fine, all went well, GRUB is back again and it recognized both Windows and Zenwalk (he called it Slackware, though... well... it
IS Slack anyway!), but I thought... I installed the wrong distro. I realy wanted to install Kubuntu 6.10 on hdb7, but put the wrong stuff to load and didn't realy care about it.
OK, so let's install Kubuntu 6.10. On to hdb7, of course. It went well... But I booted later and... Hey, where is Windows on GRUB's menu? Kubuntu is here, Zenwalk ("Slackware") also. OK, I can fix /boot/grub/menu.lst without a problem. Let's boot Kubuntu, mount hda1... it's EMPTY. oops... seems I formated it by mistake during the partition choosing for Kubuntu. This is: when you install Kubuntu (or any other *buntu) and manualy choose the partitions, you can check the partitions to be mounted if they will be formated or not. I must have accidentaly checked hda1 for formatting...
OK, no big deal. My personal files were backed up, so I didn't lose any important stuff. The Windows and softwares I can install again, and I realy am not using Windows for other stuff than playing: Linux is for everything else lately.

But... let's reinstall Windows!
Pick WinXP disc, let's boot from it... No, it doesn't. Yes, booting from CD is turned on, the CD is intact also, but it doesn't boot. So, searching around, I saw that it won't boot if GRUB is on the MBR. I have to "restore" the MBR before being able to boot the WinXP disc. Yes, there are a lot of ways to do it, I know.
But now I plan to use the whole "new" HD of 80GB to finaly do the mess I want to do. Will repartition it, etc. I will reinstall Windows XP to the slave drive, then reinstall it AGAIN when the 120GB HD comes up.
With this experience, I see I could live without a separate /boot partition.

Now, just two questions:
(1) Is there any problem to allocate hda1 for swap, or it "cannot" be the first partition?
(2) Best way to install WinXP to hdb1 after I have at least one Linux distro running on hda?
I may even run Windows inside Linux via VMware or so, but... I need to know about (2) so I can get to know the alternatives.
Thank you, specialy for the patience!