Drivers perhaps? XD
Download these files;
Mac - http://www.mediafire.com/?z8myxs9941kz3gg
Linux - http://www.mediafire.com/?m62rt943mroxm4s
Or you can download and install the Android SDK (Software Development Kit) Starter package from http://developer.android.com/sdk/index.html
You can read all about how to install the SDK at http://developer.android.com/sdk/installing.html
. Ignore all the stuff about Eclipse though, you don't need that unless you're going to start writing Android apps.
Now, from version 8 (Android 2.3) of the SDK onwards, adb has been taken out of this starter package. If you downloaded version 7 (Android 2.2), then you've already got adb and you can skip Step 3 and go straight to Step 4 below. Otherwise you need to proceed to Step 3 to add adb to the SDK.
Extract the files and rename "adb-linux" ("adb-mac") to "adb" and "fastboot-linux" ("fastboot-mac") to "fastboot"
You could call it anything you like, like "cheese" and "bread", but that makes things difficult.
Mac - Copy the files to the folder /bin
You will need to unhide the folder. Google it.
Linux - Copy the files to /system/bin *OR* /bin
I have not used Linux for ages so my folders are rotting away. I believe you will need root access to do this, I used Kongregate (I think) as an app to control my root copying needs.
On your phone, go into Menu->Settings->Applications->Development and make sure you have the entry "USB Debugging" ticked. adb will not work without this.
Plug your phone into your PC using the original HTC cable. This is important, do not use a third-party cable since it might not work with adb (even though it might seem fine with other communication with your phone). Or whatever.
Open a Terminal window. On your PC/Mac. To emphasise, you are running this on your PC, not directly from your phone (e.g. terminal emulator) :
The part were it says "Dan-Wilsons-MacBook:~ danwilson$" will probably not be on your PC/Mac, unless you are called Dan Wilson, and have a MacBook.
Dan-Wilsons-MacBook:~ danwilson$ adb devices
This should display something like the following :
List of devices attached
... where the "XXX12345" bit is actually your phone's serial number. If the list is blank and the phone is plugged in ok, go back to Step 6 and make sure USB Debugging is enabled. If you can see your phone, YOU WIN A CHEESECAKE!
If you decided to be awkward and call "adb-linux" ("adb-mac") "cheese", replace the word "adb" in command lists (like the above) to "cheese". It looks cool but complicates things.
Dan-Wilsons-MacBook:~ danwilson$ cheese devices
I think this looks OK. Some bits are weird and I don't know about drivers, but still, better than nothing. It is rough, but I've not done it in ages. Sorry bout that.
Here is the adb and fastboot files for Windows. Check they work with the Z before throwing them in the first post. If you do.