Determine If File Is Packed Or Had Filetype Changed

Stop to try to compare pac to something other...each pac is different and u have to find how it's composed.
The best luck u can have it's if there is a TOC and a pointer table at the beginning of the file but I don't think it's the case here. You have the worst (and the most common) version...just one file after the other.
Now or you are right and u have the file size after the LZS or try to extract everything between a "lzs" and another.
I doubt that there are some bytes that tell you if the file is text or graphics...more if it's compressed or not.
Your question about "how i decompress it?? " let me perplex, you don't know how compression in general works??
http://en.wikipedia.org/wiki/LZ77_and_LZ78 here some general information.
More specific but just remember that it doesn't have to be exactly the same can be found here:
http://wiki.qhimm.com/FF7/LZS_format

The PAC files can be figured out pretty easily.

PAC file header

Offset	Size	Description.
0x0000	Word	Magic bytes 'add ' 61 64 64 00.
0x0004	Word	Version? Name alignment? Always 04.
0x0008	Word	Version? File alignment? Always 20.
0x000C	Word	Start of Index Table? Always 0x20.
0x0010	Word	Number of entries in table.
0x0014	Word	Filler? Always 0x0000.
0x0018	Word	Filler? Always 0x0000.
0x001C	Word	Filler? Always 0x0000.

PAC file table

Offset	Size	Description.
0x0000	Word	File start offset.
0x0004	Word	Always 0x0000. Might be part of start offset.
0x0008	Word	File flags?
0x000C	Word	File name offset. File name is zero-terminated ASCII.
0x0010	Word	Always 0x0000. Might be part of name offset.
0x0014	Word	Filler? Always 0x0000.
0x0018	Word	Filler? Always 0x0000.
0x001C	Word	Filler? Always 0x0000.
0x0020	Word	Filler? Always 0x0000.

With that info you can extract files from the packed archive.

Now for the LZS files themselves:

PAC file header

Offset	Size	Description.
0x0000	Word	Magic bytes 'LZS ' 4C 5A 53 00.
0x0004	Byte	Version? Always 05.
0x0005	Byte	Version? Always 05.
0x0006	Byte	Version? Always 08.
0x0007	Byte	Version? Always 00.
0x0008	Word	Start offset compressed data.
0x000C	Word	Offset of data end?
0x0010	Word	Uncompressed file size?
0x0014	Word	The LZS file's size.
0x0018	Word	Version? Size? Always 0x0200.
0x001C	Word	Filler? Always 0x0000.
0x0020	Variable	Zero-terminated file name.

The pointer to data-end one is somewhat of a mystery for me. It points directly into the stream and often, but not always, MIG.00.1PSP (CS1Nanoha_BarrelShotLight01_8b.tga) or OSG.00.1PSP (CS1Nanoha_SLB.gso). However, sometimes there's nothing of interest there, like in MakerLogo.pac's MakerLogo.spr.

It was suggested that I link some of the file so I have uploaded some to megaupload if anyone wants to look at them to help me in figuring out how they are compressed. The link is here

Oh and thanks Tauwasser for the info.