Glad you've sorted the activation problem for now!
Partitioning the remaining space on the drive :
1. Go the Run command on your Start menu & type in diskmgmt.msc
2. When Disk management has opened, you should see a graphical representation (like a bar chart) of your 80GB drive. It should indicate that there is a 20GB partition (C drive) & 60GB (approx) of unallocated space.
3. Right click on the unallocated space, & select create partition from the drop down menu.
4. When the wizard starts, select 'Extended partition', make sure you tell it to use all the available space & follow the instructions.
5. When completed, you will see your 20GB partition with the new extended partition next to it. Right click on the extended partition & select create partition again.
6. This time you will create a logical partiton. Make sure you use all the available space, assign a drive letter to it & tell it to format the partition using NTFS.
7. When the wizard closes, wait while the partition is formatted. This may take a little while & you will see a counter marking the progress. When this reaches 100%, you can close disk management & the partition is ready to use
NB THESE INSTRUCTIONS ARE BASED ON WIN2000 VERSION. XP WILL BE THE SAME BUT IF IT DOESN'T GIVE YOU THE OPTION TO CREATE AN EXTENDED PARTITION (STEP 4) THEN JUST JUMP TO STEP 6.
Re. the memory upgrade :
Before you buy any more memory, go to www.crucial.com & use their memory advisor. Select your computer from the list & it will tell you exactly which ram is compatible with your system.
Re. your activation & new hardware question :
This is a quote from Microsoft that should answer that for you :
"How does product activation determine tolerance? In other words, how many components of the PC must change before I am required to reactivate?
Common changes to hardware such as upgrading a video card, adding a second hard disk drive, adding RAM or upgrading a CD-ROM device will not require the system to be reactivated.
Specifically, product activation determines tolerance through a voting mechanism. There are 10 hardware characteristics used in creating the hardware hash. Each characteristic is worth one vote, except the network card which is worth three votes. When thinking of tolerance, it's easiest to think about what has not changed instead of what has changed. When the current hardware hash is compared to the original hardware hash, there must be 7 or more matching points for the two hardware hashes to be considered in tolerance. If the network card is the same, then only 4 additional characteristics must match (because the network card is worth 3, for a total of 7). If the network card is not the same, then a total of 7 characteristics other than the network card must be the same. If the device is a laptop (specifically a dockable device), additional tolerance is allotted and there need be only 4 or more matching points. Therefore, if the device is dockable and the network card is the same, only one other characteristic must be the same for a total vote of 4. If the device is dockable and the network card is not the same, then a total of 4 characteristics other than the network card must be the same.
Are the changes cumulative? In other words, if I change one component today and one tomorrow, is that two component changes?
The changes are cumulative; however, if a user is asked to reactivate, the hardware profile is reset to that new configuration.
What are the 10 hardware characteristics used to determine the hardware hash?
The 10 hardware characteristics used to determine the hardware hash are: Display Adapter, SCSI Adapter, IDE Adapter, Network Adapter MAC Address, RAM Amount Range (i.e. 0-64mb, 64-128mb, etc), Processor Type, Processor Serial Number, Hard Drive Device, Hard Drive Volume Serial Number, CD-ROM/CD-RW/DVD-ROM. "