File splitting in Linux

Open the Terminal Window & type:
$ split --help
By default it splits every 1000 lines. You can use the '-l' option and try other options.
Choose one which suits your needs.

Similarly for joining files use the 'cat' command, for eg.,
$ cat Sample1.txt Examples.txt Codes.txt >> AllJoined.txt

Now open the file called 'Alljoined.txt' , it will contain the contents of all the three files
Sample1.txt, Examples.txt, Codes.txt!!

I want to split large images like iso especially dvd images so i can carry in one or more cds. does this utilities works for them, especially for large files.

Yes, ofcourse it will work with any file format. If you want to split a large ISO image (DVD)
format, then calculate how many lines it contains. Suppose there are N number of
lines and you want to split the file into 3 files (ie., N/3). Then you have to specify the
value of N in the options. For eg.,
split --lines=6000
There are very good file splitting & joining software available for Windows.
Try 'File Splitter Deluxe' for splitting & joining large files.
Get it from here: *www.softdd.com/filesplt/index.htm
You better use the above software. If you use Linux tools, then you must be thorough with it.
It's not recomended for beginners to use these command-line tools.