When you enter into the game on your character and the game crashes, are you testing all of this on one character? Your character may have gotten stuck going through a portal or map, thus causing the crashes to occur.
When you install the item pack, are you putting the files in the correct folders and replacing them when asked to do so? If you are skipping over those files that it asks to replace, this can cause issues.
It's possible that your computer simply cannot handle the lag that is produced by the effect of the items. If the character(s) that you're logging onto is in a crowded area with many users around, this can increase that lag that you're getting, especially when these users have items on their characters.