兩個hdd係xp入面點可以一齊用

First step refer to (shampoo)'s answer set second HD to slave.
If your HD cable have master and slave written on it you should set both HD to cable select.
Method of setting is written on the HD label.
With this your mother board will see 2 HD

second part

This is because of NTFS format of Win XP HD if use FAT 32 no problem. WinME use Fat32 so no problem.
To fix problem DO NOT USE FORMAT A機有win xp的harddisk 100% DO NOT FORMAT

For NTFS formated HD of WinXP,
1)after windows start up you right click MY COMPUTER
2)Click Manage, to run Computer management
3)In Computer management you choose Disk Management
4) Then on the lower right window you will see Disk 0/Disk 1 /CD-rom 0 etc.
5)Disk 0= C-drive= 正常的win xp B機(B 是Primary master)
Disk 1= Primary Slave=A機有win xp的harddisk
Disk 1 will say unallocate or something, right click on Disk 1 and choose IMPORT or re-start ( you may need to give it drive letter as well)
Then you will see your old HD in file manager
***remember NOT to click on convert or format.
6)IF ou do not see thing say in 5) above, you may have set the cable incorrect

PS.
Sometimes using a external box is easier but still need to do step 5 above.

你有無插過個hd 的針仔呀
重要用黎裝windows 行個個hd 唔駛轉,
但另一個hd 要改番d 針做副hd 先可以用架