Many newer MBs still have an IDE connector so I'm assuming yours doesn't. I don't know of another way to connect internally unless you could find a PCI board with an IDE interface. Why are you so resistant to an external enclosure?
Hawkeye22 has pointed you in the right direction - an adapter that plugs into the IDE drive's back connector and converts it into a SATA-connected device you can hook up to one of your empty SATA ports.
As far a physical mounting inside your case is concerned, you usually would have three options (depending on your case):
1. Mount in an empty 3½" drive slot just like any other HDD.
2. Mount in a front-accessible 3½" drive slot (like what is used for a 3½" floppy drive), and don't remove the slot front cover.
3. Mount in a larger 5¼" front-accessible slot and don't remove the slot front cover. However, in this case you will need to obtain a pair of adapter rails that fasten onto the 3½" HDD and make it wide enough to fit the 5¼" slot. If these are hard to find, check out shops with used computer parts - rails like this have been used also for mounting old tape drives in 5¼" slots.
Check on one thing. If you choose a 5¼" slot, many of those are near the top of the case, and the cable run down to your mobo's SATA port may be longer than a common SATA data cable - you might need to get one a little longer than usual.
i count 6 drives. 4 external, new one with OS on it, and now an old IDE.
just an idea, king of rock, why not just get one HDD big enough for everything?
besides, the longer you keep old drives running the more you're just pushing your luck that they'll keep working. how old is this IDE drive anyways?
I HEAR that! All good points, and what I have considered myself, but since I back up everything anyway, and since they are just files, I figured it would be easier/cheaper than getting a new 250gb internal drive...
...of course, I am saving a little $$$, adapter is like $17. and new drive would be around $35...I guess it comes down to being attached/stubborn about my old drive!
(I am quite sure I am not the first ol' timer experiencing that phenomenom)