i wanna install windows application in Ubuntu. and deceded to use the playinlinux. its safe for me ? any problm ?
No . Using PlayonLinux is completely safe.
1.2. Does Wine hurt Linux or other free operating systems?
Wine increases the usefulness of Linux, makes it easier for users to switch to free operating systems, and for Windows developers to make applications that work on them.
11.2. How good is Wine at sandboxing Windows apps?
Wine does not sandbox in any way at all. When run under Wine, a Windows app can do anything your user can. Wine does not (and cannot) stop a Windows app directly making native syscalls, messing with your files, altering your startup scripts, or doing other nasty things.
Wine also has a separate Wine "myths" page where you can find more detail.
From experience, using both applications for a few years now I'd say that both are equally good. Also PlayOnLinux is more GUI oriented and much easier to use for those who just get started.
You can also check the Wine (AppDB) - Wine Application Database, to see if the application you are attempting to install runs on your system/setup, based on other users past experiences and the same option is available for PlayOnLinux - Supported Software.
In the end it is best to make your own experiences and yes, it is safe to use, since both applications came a long way, are well developed and regularly attended for.
To install see here: Ubuntu Apps Directory