[Desire Android Development] sibere:
type just /system/xbin/busybox. You'll get a list of commands. If mkswap is not in the list, it means that you didn't installed the latest busybox properly.

you shoud get this:

busybox
BusyBox v1.17.2 (2010-09-05 04:15:58 CDT) multi-call binary.
Copyright (C) 1998-2009 Erik Andersen, Rob Landley, Denys Vlasenko
and others. Licensed under GPLv2.
See source distribution for full notice.

Usage: busybox [function] [arguments]...
or: function [arguments]...

BusyBox is a multi-call binary that combines many common Unix
utilities into a single executable. Most people will create a
link to busybox for each function they wish to use and BusyBox
will act like whatever it was invoked as.

Currently defined functions:
[, [[, acpid, addgroup, adduser, adjtimex, arp, arping, ash, awk,
basename, beep, blkid, bootchartd, brctl, bunzip2, bzcat, bzip2, cal,
cat, catv, chat, chattr, chgrp, chmod, chown, chpasswd, chpst, chroot,
chrt, chvt, cksum, clear, cmp, comm, cp, cpio, crond, crontab, cryptpw,
cttyhack, cut, date, dc, dd, deallocvt, delgroup, deluser, depmod,
devmem, df, dhcprelay, diff, dirname, dmesg, dnsd, dnsdomainname,
dos2unix, du, dumpkmap, dumpleases, echo, ed, egrep, eject, env,
envdir, envuidgid, ether-wake, expand, expr, fakeidentd, false, fbset,
fbsplash, fdflush, fdformat, fdisk, fgconsole, fgrep, find, findfs,
flock, fold, free, freeramdisk, fsck, fsck.minix, fsync, ftpd, ftpget,
ftpput, fuser, getopt, getty, grep, gunzip, gzip, halt, hd, hdparm,
head, hexdump, hostid, hostname, httpd, hush, hwclock, id, ifconfig,
ifdown, ifenslave, ifplugd, ifup, inetd, init, insmod, install, ionice,
ip, ipaddr, ipcalc, ipcrm, ipcs, iplink, iproute, iprule, iptunnel,
kbd_mode, kill, killall, killall5, klogd, last, length, less, linux32,
linux64, linuxrc, ln, loadfont, loadkmap, logger, login, logname,
logread, losetup, lpd, lpq, lpr, ls, lsattr, lsmod, lspci, lsusb,
lzcat, lzma, lzop, lzopcat, makedevs, makemime, man, md5sum, mdev,
mesg, microcom, mkdir, mkdosfs, mke2fs, mkfifo, mkfs.ext2, mkfs.minix,
mkfs.vfat, mknod, mkpasswd, mkswap, mktemp, modinfo, modprobe, more,
mount, mountpoint, mt, mv, nameif, nc, netstat, nice, nmeter, nohup,
nslookup, ntpd, od, openvt, passwd, patch, pgrep, pidof, ping, ping6,
pipe_progress, pivot_root, pkill, popmaildir, poweroff, printenv,
printf, ps, pscan, pwd, raidautorun, rdate, rdev, readahead, readlink,
readprofile, realpath, reboot, reformime, renice, reset, resize, rev,
rm, rmdir, rmmod, route, rpm, rpm2cpio, rtcwake, run-parts, runlevel,
runsv, runsvdir, rx, script, scriptreplay, sed, sendmail, seq, setarch,
setconsole, setfont, setkeycodes, setlogcons, setsid, setuidgid, sh,
sha1sum, sha256sum, sha512sum, showkey, slattach, sleep, smemcap,
softlimit, sort, split, start-stop-daemon, stat, strings, stty, su,
sulogin, sum, sv, svlogd, swapoff, swapon, switch_root, sync, sysctl,
syslogd, tac, tail, tar, tcpsvd, tee, telnet, telnetd, test, tftp,
tftpd, time, timeout, top, touch, tr, traceroute, traceroute6, true,
tty, ttysize, tunctl, udhcpc, udhcpd, udpsvd, umount, uname, unexpand,
uniq, unix2dos, unlzma, unlzop, unxz, unzip, uptime, usleep, uudecode,
uuencode, vconfig, vi, vlock, volname, wall, watch, watchdog, wc, wget,
which, who, whoami, xargs, xz, xzcat, yes, zcat, zcip