via http://www.psp-hacks.com/2011/04/13/...8-me-released/

If you’re a PSP-2000 owner and want the absolute latest in official firmware, yet you wish to keep ISOs and [unsigned] homebrew functional, then I reckon you check out neur0n’s latest CFW: 6.38 ME v1. But before you do that — make sure your Pandora battery and magic memory stick is on standby — “the degree of stability is unknown at this time.”
Install
  1. Install CFW or HEN (i.e. 5.00 M33, 6.20 TN, 6.35 PRO-B3, 6.37 ME)
  2. Copy the UPDATE folder to ms0:/PSP/GAME/
  3. Copy the official 6.38 update to ms0:/PSP/GAME/UPDATE/638.PBP
  4. Run 6.38 ME v1 installer from XMB

Features
  • Access recovery console by pressing and holding R-Trigger on boot
  • Boot 6.38 OFW by pressing and holding “Home” button on startup
Download Here