Windows XP 32-Bit will address 4GB of memory and 4GB only, even with the PAE enabled. It is true that with PAE it is possible on 32-bit OSes to address more than 4GB of memory. However, Microsoft has limitted XP 32-bit to 4GB of RAM regardless of if PAE is enabled or not. They did this for driver compatibility. Read
Here.
Now, the addressed space includes graphics card memory, and any memory on any devices connected to the system. This usually leaves 3.75GB or less available to address system RAM. If you have 2 HD4870x2's for instance, you will have less than 2GB available.
Now, as for the XP vs. Vista file transfer speeds, use Robocopy if you are going to move large files in Vista and it will help with the slow file copy issues. SP1 definitely helps the situation as Microsoft reworked the file transfer methods with SP1, however it isn't up to XP speeds, and probably never will be. However, it is very livable.
Edit:
Ok, this thread got me kind of interested, so I ran some tests.
System Specs:
Q6600@3.2GHz
eVGA 780i A1
4GB G.Skill PC2-1100 5-5-5-15 @ PC2-800 4-4-4-12
500GB Seagate 7200.10 16MB Cache SATA 3.0Gb/s Drive
400GB Western Digital RE2 16MB Cache SATA 3.0Gb/s Drive
I setup a test folder that was 5.39GB(5.40GB on Disk) with 762 Files ranging in size from 2MB up to 933MB in 22 folders. Multiple files types were used: pictures, movies, MP3s, zip/rar, exe, text documents.
I ran 4 tests on each OS:
Same Drive Copy-I copy the folder from one location(Desktop) to another location on the same drive(C:\). This was done on the Seagate drive.
Different Drive Copy-I copy the folder from one location to another location on a different drive. The files were copied from the Seagate drive onto the Western Digital drive.
Delete-I used the Shift+Del command to delete the folder, this directly deletes the files, avoiding the Recycle Bin. This was done on the Seagate Drive.
Robocopy-I used the Robocopy command in a cmd prompt to copy the folder from one location to another location on a different drive. The files were copies from the Seagate drive onto the Westner Digital drive.
I timed each action using a stop watch from the moment I issued the command until the transfer/delete window disappeared.
Results(m:ss format):
Vista Same Drive Copy: 3:50
Vista Different Drive Copy: 1:55
Vista Delete: Virtually Instant(A window doesn't even appear, the folder just instantly disappears)
Vista Robocopy: 2:31
XP Same Drive Copy: 3:52
XP Different Drive Copy: 2:02
XP Delete: Virtually Instant(A window does appear, but disappears in less than a second)
XP Robocopy: 2:22
I was actually surprised by the results. Vista seems to be ever so slightly faster than XP when using explorer to issue commands, but slower with Robocopy. Either way, it seems Robocopy is the slowest method, but actually seems the fastest to me. Maybe this is because of the way the window shows progress, it shows the percentage of each file as it goes through the list of files. XP still seemed faster to me, even with the stop watch telling me otherwise. The only thing I can guess is that the XP transfer window tricks us into believing this. The Vista window is kind of dull and boring to watch, it just gives you the source and destination, and the stupid box animation at the top. The XP window lists each file as it is copied, and gives the nice animation of the file moving from one folder to the next. Because the XP box is a little more entertaining than the Vista transfer window, it tricks us into thinking it is moving faster(time flies when you are having fun type of deal). And Robocopy does the same type of trick, because it lists each file, and counts the percentage of the file that is currently be transferred, it is kind of fun to watch, and probably why it seems to go the quickest, even when it is actually slower.
