hi guys,

i want to use some commands from winXP in 98se such as "net send" command
how to add this command if it possible??

Depends on which command(s) u want to use.

For example NET exists in all 9x OSes, but an NTx command line switch like SEND is not valid in 9x OSEs.
To learn all valid NET options, run:

net /?

Other command line tools that exist, with more or less similar NTx functionality in 9x:

CHOICE.COM
COMMAND.COM
DISKCOPY.COM
DOSKEY.COM
EDIT.COM
FORMAT.COM
KEYB.COM
MODE.COM
MORE.COM
SYS.COM
WIN.COM
ARP.EXE
ATMADM.EXE
ATTRIB.EXE
CARDDRV.EXE
CHKDSK.EXE
CLSPACK.EXE
CMSTP.EXE
CSCRIPT.EXE
CVT.EXE
DEBUG.EXE
DELTREE.EXE
DITRACE.EXE
DOSMGR.EXE
EMM386.EXE
EXTRAC32.EXE
EXTRACT.EXE
FC.EXE
FDISK.EXE
FIND.EXE
FTP.EXE
IEXTRACT.EXE
IPCONFIG.EXE
JVIEW.EXE
LABEL.EXE
MEM.EXE
MOVE.EXE
MSCDEX.EXE
MSDLC.EXE
NBTSTAT.EXE
NET.EXE
NETSTAT.EXE
NLSFUNC.EXE
PING.EXE
PROTMAN.EXE
REGEDIT.EXE
REGSVR32.EXE
ROUTE.EXE
RUNDLL.EXE
RUNDLL32.EXE
RUNONCE.EXE
SCANDISK.EXE
SCANREG.EXE
SELECT.EXE
SETUP.EXE
SETVER.EXE
SMARTDRV.EXE
SORT.EXE
START.EXE
SUBST.EXE
SULFNBK.EXE
TCMSETUP.EXE
TELNET.EXE
TRACERT.EXE
WALIGN.EXE
WJVIEW.EXE
XCOPY.EXE
XCOPY32.EXE

All files listed above are found on the Windows 98 SE setup CD [example], mostly inside CABs.
Most should be already installed in %windir% or %windir%\system , which means u don't need to type their path names whenever u execute them.
Run them with /? to view their valid options.
Some of these tools work from outside Windows [native/true MS-DOS mode], some work only from within Windows GUI [DOS box], and some work [exclusively] from within CONFIG.SYS or/and AUTOEXEC.BAT.

There are also several internal DOS commands built into COMMAND.COM:

CD
COPY
DATE
DEL
DIR
MD
REN
TIME
VOL
etc...

More details:
SETUP:
http://www.mdgx.com/last2.htm#SETUPSW
SCANREG:
http://www.mdgx.com/98-1.htm#SCANREG98
Windows 98 + 98SE tools:
http://www.mdgx.com/98-1.htm#98ESS
EXTRACT:
http://www.mdgx.com/newtip15.htm#CABEX
SMARTDRV:
http://www.mdgx.com/newtip2.htm#OUTSMART
MS-DOS tools undocumented switches:
http://www.mdgx.com/secrets.htm

Besides the MS commands bundled with your OS, you can also find many other [similar] ones on the net [most are free(ware)]:
http://www.mdgx.com/dos.htm

Hope this helps.