Below is my hdd config

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ATA133 PCI Raid Card

Primary Master - 80GB HDD
Primary Slave - 80GB HDD
Both running as Raid 0

Secondary Master - 160GB HDD

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Mobo IDE Controller

Primary Master - CDRW
Primary Slave - 6GB HDD (Slackware installed to this HDD)
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root@slacker:/# fdisk -l

Disk /dev/hdg: 164.6 GB, 164696555520 bytes
255 heads, 63 sectors/track, 20023 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Device Boot Start End Blocks Id System
/dev/hdg1 2 20023 160826715 f W95 Ext'd (LBA)
/dev/hdg5 2 8925 71681998+ b W95 FAT32
/dev/hdg6 8926 17849 71681998+ b W95 FAT32
/dev/hdg7 17850 20023 17462623+ b W95 FAT32
Warning: ignoring extra data in partition table 5
Warning: ignoring extra data in partition table 5
Warning: ignoring extra data in partition table 5
Warning: invalid flag 0x2588 of partition table 5 will be corrected by w(rite)

Disk /dev/hde: 80.0 GB, 80026361856 bytes
255 heads, 63 sectors/track, 9729 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Device Boot Start End Blocks Id System
/dev/hde1 * 1 2550 20482843+ 7 HPFS/NTFS
/dev/hde2 2551 19458 135813510 f W95 Ext'd (LBA)
/dev/hde5 ? 77941 2524 1541696845+ 11 Hidden FAT12

Disk /dev/hdf: 80.0 GB, 80026361856 bytes
255 heads, 63 sectors/track, 9729 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Disk /dev/hdf doesn't contain a valid partition table

Disk /dev/hdb: 6400 MB, 6400235520 bytes
255 heads, 63 sectors/track, 778 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Device Boot Start End Blocks Id System
/dev/hdb1 * 1 729 5855661 83 Linux
/dev/hdb2 730 778 393592+ 82 Linux swap
root@slacker:/#

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Questions:

1) How do I mount my RAID 0 partitions? Tried hde and sd0/1, both also cannot.

Assuming you have the correct driver/demon installed, you should first set up your /etc/raidtab in order to match your configuration.
A possible one could be
raiddev /dev/md0
raid-level 0
nr-raid-disks 2
persistent-superblock 1
chunk-size 4
device /dev/hd(x)
raid-disk 0
device /dev/hd(y)
raid-disk 1

now
mkraid /dev/md0

should initialize the disks battery

then the battery can be formatted, mounted or whatever you like.
In order to check if the battery is correctly working try
cat /proc/mdstat
if you are using a 2.6 kernel the log status could be found on
/sys/mdstat (not sure since I'm still using the 2.4.22 kernel)
Ciao

Will doing that destroy my current raid or whatsoever?

I already have my raid disk partition nicely and data are in place. Slackware did recognise my Sil0680 raid card when booting up though.

RAID is basically a method to safely store your dates.
Raid level 0 (striping) can also be used to improve performances of your hard disks.
It is strongly recommended you have your "basic system partitions" such as /,/usr,/sbin outside of the RAID system as it is hardly managed at boot (unless you use a tricky method).
In other word , avoid having you system files on RAID partition, if you can....(it seems you can)
It is also recommended you have your hard drives not installed on the same IDE bus as IDE transporter cannot manage with a sufficient speed two disks on the same channel.
I understand your system is correctly supporting your RAID controller, so you're at a good point.
You need RAID tools installed. Slack 9.1 should have them installed by default.
If you don't have you should create a /etc/raidtab file on wich you tell the system your RAID configuration. You can edit the raidtab file I posted previously in order it can match your requirements.
Then you need to create a node for your RAID system by
mkraid /dev/md0
Now you have to create a filesystem on your new logic unit (this will delete all files on such units) by
mkfs -t ext2 /dev/md0
Activate the RAID driver by
raidstart /dev/md0
Create a mount point for /dev/md0 by
mkdir /opt1 or whatever you like
then you can mount the new file system by
mount /dev/md0 /opt1
Do not create an entry in your /etc/fstab since the kernel will try to mount /dev/md0 before it executes raidstart.
If you want to have your disks battery mounted at boot edit your /etc/rc.d/rc.local adding
raidstart /dev/md0
mount /dev/md0 /opt1
Ciao